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ASSAYING 


THREE  PARTS. 


Part  ist. — Gold  and  Silver  Ores;  Part  2d. — Gold  and  Silver 
Bullion;  Part  3D. — Lead,    Copper,  Tin,  Mercury, 
Zinc,  Nickel  and  Cobalt,  Also,  Appen- 
dix to   Part   ist  and   3d, 


By  C.  H.  AARON,  Metallurgist, 

author  of 
Testing   and  Working   Silver   Ores,"  "  Leaching  Gold  and  Silver  Ores. 


F^ARXS    2    AND    3 


PUBLISHED    and    SOLD    BY 

DEWEY  &CO., 

PROPRIETORS  MINING  AND  SCIENTIFIC  PRESS, 

SAN    FRANCISCO,    CAL.,   1885. 

[Copyrighted.] 


Bftncroit  library 


^l\t  %mn  mi  ^tmiiiit  ^^^m. 


SAN  FRANCISCO,  CAL., 

THE   STEADFAST   FRIEND   OF  TRUTH   AND   PROGRESS 
— AN   HONEST   PAPER, 

THIS   BOOK   IS   RESPECTFULLY   DEDICATED 
BY  THE  AUTHOR. 


CONTENTS. 

O 

^  

0 

*"  PART  TWO. 

^^  Page. 

£pEFACE 7 

tRTRODUCTION 9 

Wold  and  Silver  Bullion 13 

Apparatus 15 

Inciting  Bullion 27 

VAssaying  Bullion 36 

C           Gold  Bar 37 

^           Dor^eBar 42 

jl            Base  Bar 44 

^            Gold  and  Platinum 47 

H            Silver  Bar 49 

^            Silver  Lead 52 

|_               Value  of  Bars 53 

Humid  Assay  of  Silver 56 

Measuring  the  Normal  Solution 57 

Measuring  the  Decime  Solutions 58 

Preparing  the  Normal  Solution 59 

Preparing  the  Decime  Salt  Solution 61 

Preparing  the  Decime  Silver  Solution 62 

Standardizing  the  Normal  Solution 62 

The  Assay 67 

Correcting  the  Assay 71 

General  Remarks  on  the  Humid  Assay 72 

Recovery  of  Silver 75 

Preparation  of  Pure  Silver 75 

Recovery  of  Acid 78 

Conclusion  of  Part  Two 79 


6  CONTENTS. 

PART  THREE. 

Page. 

Manipulation,  etc 83 

Lead  Ores 89 

Fire  Assay 89 

Wet  Assay 91 

Copper  Ores 95 

Fire  Assay ,  95 

Wet  Assay 98 

Volumetric  Assays 104 

Parkes'  Process 104 

Amalgamation 107 

New  Process 107 

Preparation  of  Potassium  Zanthate 112 

Electrolytic  Determination  of  Copper  in  Ores,  etc 114 

Assaying  of  Tin  Ores 119 

Assaying  of  Mercury  Ores 121 

Assaying  of  Zinc  Ores 124 

Assaying  of  Zinc  Ores,  New  Method 126 

New  Assay  of  Nickel  and  Cobalt 128 

Assay  of  Chromium 135 

Assay  of  Bismuth 136 

Assay  of  Arsenic 138 

Assay  of  Antimony 139 

Assay  of  Sulphur 140 

Assay  of  Salt 141 

Appendix  to  Part  1 143 

Notes  on  Crucible  Assays 143 

Weighing  by  Oscillations 151 

Appendix  to  Part  III '. 155 

The  Assay  of  Lead , 155 

The  Assay  of  Copper 156 

Note 157 


PREFACE  TO  PARTS  II.  AND   III 


It  is  not  my  desire  to  produce  a  book  which  shall 
supersede  the  necessity  for  thought  on  the  part  of  the 
student.  My  intention  is  not  so  much  to  teach  people 
as  to  aid  them  in  learning.  Some  may  prefer  those 
books  in  which  they  find  everything  cut  and  dried,  as 
it  were;  take  so  much  of  this  and  so  much  of  that,  do 
thus  and  so,  without  alternative  and  without  exception, 
as  though  it  were  possible  to  give  fixed  and  positive 
rules  for  all  operations,  in  all  cases.  To  such  I  would  say, 
if  they  have  not  heads  of  their  own,  they  would  better 
turn  their  attention  to  something  else  than  an  art  which 
must  be  practiced  under  ever  varying  conditions,  and  is 
based  on  a  science  in  which  new  discoveries  are  being 
made  every  hour. 

In  the  following,  as  in  preceding  pages,  I  have  en- 
deavored to  make  as  simple  and  easy  as  possible  the 
entrance  to  what,  when  properly  appreciated  and  lov- 
ingly followed,  must  prove  a  pleasant  and  mentally  prof- 
itable study,  a  pathway  in  which  many  beautiful  flowers 
grow,  but  in  which  are  also  some  thorns;  in  which  none 


8  PREFACE. 

can  call  himself  an  unerring  guide,  and  in  which  but 
little  real  progress  can  be  made  without  hard  work. 
Assaying  is  a  beautiful  art,  the  parent,  to  a  certain  ex- 
tent, and  still  more  the  offspring,  of  the  sublime  science 
of  chemistry.  The  "practical"  assay er,  by  which  I 
mean  him  who  has  no  other  guide  than  his  own  limited 
experience,  and  such  information  as  the  writer  of  a 
hand-book  can  impart,  may  do  tolerably  wc^l  for  a 
quartz-mill,  or  small  assay  office  among  the  mines  of 
gold  and  silver;  scarcely  for  a  smelting  plant,  and  he 
will  never  realize  the  beauties,  nor  enter  the  upper  story 
of  the  edifice  in  which  he  labors,  until  he  has  acquired 
a  sound  understanding  of  the  fundamental  principles  of 
chemistry,  as  well  as  a  very  considerable  acquai>itance 
with  its  facts. 


INTRODUCTION. 


All  the  substances  in  nature  are  either  simple  or 
compound.  A  simple  substance  or  body  is  one  from 
which  nothing  different  from  itself  can  be  extracted. 
There  are  sixty-four  simple  substances  now  known,  and 
several  more  supposed.     They  are  called  elements. 

The  elements  have  a  tendency  to  combine  one  with 
another,  forming  compounds;  this  tendency  is  called  af- 
finity. The  strength  of  the  affinities  of  different  ele- 
ments differs.  The  strength  of  the  affinity  of  anyone 
element  for  any  other  differs  under  different  conditions  of 
temperature,  pressure,  electricity,  etc. 

Most  of  the  elements  are  known,  and  all  are  believed, 
to  be  capable  of  assuming  the  solid  or  the  gaseous  state; 
most  of  them  also  the  intermediate  condition  of  a  liquid. 
The  assuming  of  these  different  conditions  by  the  same 
substance  is  dependent  on  temperature  and  pressure. 

The  elements  may  be  unixed  in  any  proportions,  but 
they  combine  only  in  fixed  proportions.  When  elements 
combine  they  form  a  substance  which  has  different  prop- 
erties from  those  of  the  components.  Two  or  more  solids 
may  combine  to  form  a  liquid  or  a  gas:  two  or  more 
liquids  or  gases  may  form  a  solid,  etc.  A  knowledge  of 
the  proportions  in  which  bodies  combine,  and  of  the  con- 
ditions which  determine  their  combination  and  dissociation, 
forms  the  basis  of  chemistry. 
2 


10  INTRODUCTION. 

All  the  metals  are  elements.  Their  mixture  by  fusion 
forms  alloys.  Hydrogen,  oxygen,  nitrogen,  chlorine, 
bromine,  iodine,  carbon,  sulphur,  selenium,  phosphorous 
boron,  silicon,  are  elements  which,  with  the  metals,  enter 
into  the  composition  of  the  ores,  fluxes,  etc.,  which  come 
under  the  notice  of  the  assay er. 

The  fact  that  the  elements  combine  only  in  fixed  pro- 
portions, is  the  reason  why  a  certain  quantity  of  com- 
bustible matter  produces  only  a  certain  quantity  of  lead 
from  litharge  in  an  assay.  The  element  lead  (a  metal) 
combined  with  the  element  oxygen  (a  gas)  in  the  exact 
proportion  of  103.56  parts  by  weight  of  lead  to  8  parts 
by  weight  of  oxygen,  forms  111.56  parts  of  litharge. 
Lead  combines  with  oxygen,  under  certain  conditions,  in 
two  other  proportions,  but  the  resulting  compounds  are 
not  litharge,  and  the  proportions  are  definite  and  un- 
changeable in  each,  combining  spontaneously  under  proper 
conditions,  and  any  excess  of  either  element  remaining 
separate. 

The  element  carbon  also  combines  with  oxygen,  6 
parts  of  the  former  and  16  of  the  latter,  forming  22 
parts  of  the  gas  commonly  called  carbonic  acid  gas  (now 
called  carbon  dioxide).  Under  the  action  of  heat,  the 
affinity  of  carbon  for  oxygen  is  greater  than  the  affinity 
of  lead  for  oxygen.  Hence  if  litharge  and  carbon  are 
heated  together,. the  carbon  takes  oxygen  from  the  litharge 
and  sets  lead  free.  But  this  action  can  only  take  place 
between  definite  proportions  of  the  substances.  If  twice 
111.56  grains  of  litharge,  containing  16  grains  of  oxygen, 
be  heated  together  with  6  grains  of  carbon,  the  carbon 
takes  all  the  oxygen,  forming  22  grains  of  carbonic  acid 


INTRODUCTION.  11 

gas,  and  the  whole  of  the  lead  is  set  free ;  but  if  more 
litharge  had  been  present  that  additional  portion  would 
have  remained  unchanged.  From  this  we  see  that  6 
grains  of  carbon  reduce  223.12  grains  of  litharge,  setting 
free  207.12  grains  of  lead,  or  1  grain  of  carbon  produces 
34.52  grains  of  lead  from  litharge. 

Hydrogen,  sulphur,  iron,  and  many  other  substances 
take  oxygen  from  litharge  under  heat,  in  different  but 
fixed  proportions  for  each.  Charcoal  is  slightly  impure 
carbon,  and  1  grain  liberates  only  about  30  grains  of  lead 
from  a  corresponding  quantity  of  litharge.  Flour  con- 
tains both  carbon  and  hydrogen,  but  as  it  also  contains 
oxygen  and  nitrogen  it  is  less  efficient,  weight  for  weight, 
than  charcoal,  as  a  reducing  agent:  one  grain  liberates 
about  15  grains  of  lead.  It  is  preferable  to  charcoal  for 
assaying  because  it  is  cleanly  and  in  fine  powder. 

Nitre  consists  of  nitrogen,  oxygen,  and  potassium. 
When  heated  it  gives  ofi"  a  part  of  its  oxygen,  and  if 
lead  is  present,  litharge  is  formed,  the  quantity  of  lead  so 
transformed  depending  on  the  quantity  of  the  nitre  in  ac- 
cordance with  the  law  of  definite  proportions.  If  sulphur 
or  carbon  be  also  present,  the  oxygen  combines  with  that, 
because  the  affinity  is  stronger  than  for  lead. 

(.'ompounds  can  combine  with  other  compounds,  form- 
ing new  compounds.  The  alkaline  carbonates  used  in 
assaying  are  compounds  of  the  metal  elements  sodium  or 
potassium  with  oxygen  and  carbonic  acid.  Quartz  (silica) 
is  a  compound  of  silicon  with  oxygen.  When  quartz  is 
heated  in  contact  with  an  alkaline  carbonate,  the  latter 
is  decomposed,  not  into  its  elements,  but  into  car- 
bonic acid  gas,  which  escapes  with  effervescence,  and 
sodium  or  potassium  oxide,  which  combines  with  thequartz 


12  INTRODUCTION. 

— a  compound  with  a  compound — forming  glass.  Thus 
quartz,  which  is  not  fusible  at  any  common  furnace  heat, 
is  converted  into  an  easily  fusible  substance. 

One-fifth  part  of  the  air  consists  of  oxygen,  the  other 
four-fifths  of  nitrogen.  They  are  only  mixed,  not  com- 
bined. Melted  lead  has  a  strong  afiinity  for  oxygen, 
which  it  takes  readily  from  the  air  in  such  proportion  as 
to  form  litharge.  Gold  and  silver  at  the  heat  of  melted 
lead  do  not  combine  with  oxygen.  Hence,  when  an  alloy 
of  lead,  gold,  and  silver  is  melted  in  air,  the  lead  oxidizes, 
the  gold  and  silver  do  not.  If  the  litharge  is  removed  as 
it  is  formed,  all  the  lead  is  finally  separated  from  the 
precious   metals.     This  is  the  philosophy  of  cupellation. 

When  silver  is  placed  in  nitric  acid,  it  develops  an  af- 
finity for  a  compound  of  nitrogen  and  oxygen  which  ex- 
ists in  the  acid.  Gold  does  not,  hence  when  an  alloy  of 
gold  and  silver  is  boiled  in  nitric  acid,  the  silver  forms  a 
combination  known  as  nitrate  of  silver,  which  is  soluble 
in  water,  and  if  the  acid  is  somewhat  dilute,  all  the  silver 
is  dissolved  while  the  gold  remains.  From  the  law  of 
combination  in  definite  proportions,  it  is  necessary  that 
the  acid  be  present  in  sufficient  quantity,  otherwise  a  por- 
tion of  the  silver  remains  unaltered.  If  more  than  the 
requisite  quantity  be  used,  the  excess  of -acid  remains  un- 
changed. In  practice,  the  alloy  must  contain  at  least 
twice  as  much  silver  as  gold,  otherwise  the  insoluble  gold 
so  envelopes  the  silver  as  to  protect  it  from  the  action  of 
the  acid,  except  superficially. 

Thus  the  art  of  assaying  is  dependent  on  the  laws 
of  chemistry,  and  although  it  ,piay  be  practised  with  con- 
siderable success,  it  cannot  be  properly  understood  unless 
those  laws  are  studied. 


PART  II. 
GOLD  AND  SILVER  BULLION, 


In  the  assay  of  bullion,  as  in  that  of  ore,  the  first  step 
is  to  obtain  a  correct  sample.  For  this  reason  it  is 
desirable  that  the  bars  or  ingots  should  be  made  in  the 
establishment  in  which  they  are  assayed.  It  is  not  often 
that  an  assayer  will  place  his  stamp  on  a  bar  without 
knowing  to  a  certainty  that  the  bar  is  what  it  purports 
to  be.  Moreover,  the  best  sample  is  one  that  is  taken 
from  the  molten  metal,  though  this  is  not  practised  in 
the  case  of  gold  bullion,  and  it  often  happens  that  a  lot 
of  silver  lead  in  bars,  which  in  this  country  is  called  "base 
bullion,"  must  be  sampled  without  melting  for  the  pur- 
pose. Silver  bullion  is  sampled  when  melted,  before  cast- 
ing. Silver  lead  is  so  sampled  when  practicable.  Gold 
bullion,  or  base  bullion  in  bars,  is  sampled  by  "  chip- 
ping."* 

Gold  bullion  is  assayed  by  inquartation,  involving  cu- 
pel lation,  and  parting  (Part  1,  page  74);  silver  bullion 
by  cupellation  (Parti,  page  66),  or  by  the  humid  nfiethod; 
silver  lead  by  cupellation,  sometimes  preceded  by  scoriti- 
cation. 

Bars  of  bullion    are   called  gold,  dor^,  silver,  or  base- 

*Silver  bars  are  also  chipped  when  the  metal  has  been  ladled  into  the 
moulds  from  a  refining  hearth. 


14  ASSAYING   GOLD 

The  first  consist  almost  entirely  of  gold,  with  a  little 
silver  and  sometimes  a  very  little  base  metal.  They  are 
stamped  with  the  gold  fineness  and  value  only,  the  silver 
being  allowed  for  in  the  market  price.  The  second  con- 
tain a  large  proportion  of  gold,  a  considerable  proportion 
of  silver,  and  sometimes  a  little  base  metal.  Silver  bars 
are  such  as  consist  mainly  of  silver  with  little  or  no  gold, 
nor  an  excess  of  base  metal.  Base  bars  contain  a  large 
proportion  of  base  metal,  usually  lead  or  copper.  Dore'e, 
silver,  and  base  bars  are  stamped  with  the  fineness  and 
value  of  the  gold  and  of  the  silver.  Gold  bars  containing 
more  than  an  insignificant  percentage  of  base  metal,  al- 
though not  enough  to  degrade  them  to  the  rank  of  base 
bars,  are  marked  B,  or  Base,  in  addition  to  the  gold  fine- 
ness and  value.  Such  are  the  rules  of  commercial  assay- 
ing on  the  Pacific  Coast,  at  least. 

In  order  to  extend  the  business  of  ore  assaying  to  bul- 
lion assaying  also,  certain  additional  apparatus  must  be 
provided  as  follows: — 


AND   SILVER  BULLION. 


15 


APPARATUS. 


Melting  F  urnace. — A  melting  furnace  suitable  for  light 

work    may   be 


bought  ready 
made,  and  is 
similar  to  the 
crucible  f  u  r  - 
nace  for  ore  as- 
s  ay  s .  For 
heavy  work, 
such  as  casting 
large  bars,  it  is 
best  to  build  a 
furnace  of  ma- 
son  ry ,  and , 
though  not  cus- 
tomary, it  is  ad- 
vantageous t  o 
have  it  sunk  in 
the  ground  to 
within  about  a 

Scale,  i  Inch  =  1  Foot.  f OOt  of   the    top. 

The  accompanying  diagrams  and  description,  from 
"Leaching  Gold  and  Silver  Ores,"  represent  an  excellent 
melting  furnace,  which  the  writer  has  built  in  silver  mills. 


16'  ASSAYING   GOLD 

This  furnace  is  suitable  for  a  number  30  or  35  black- 
lead  pot,  with  charcoal  as  fuel.  There  is  no  heavy  and 
expensive  cast-iron  plate  on  the  top,  and  the  cover  may 
be  of  sheet-iron,  although  cast-iron  is  better. 

The  interior  may  be  cylindrical,  but  is  better,  as 
shown  in  the  figures,  narrowed  toward  the  top  and  bot- 
tom. The  grate  bars  rest  on  an  iron  ring,  Figure  3r 
supported  by  an  offset  in  the  masonry.  The  latter  is 
mostly  of  a  very  rough  kind,  as  the  furnace  is  sunk  in 
the  ground  to  within  a  foot  of  the  top,  which,  besides 
affording  great  convenience  in  working,  obviates  the 
necessity  of  iron  bands  or  stay-rods  to  support  it  against 
the  expansion  caused  by  the  heat.  The  greater  part  of 
the  lining,  4  inches  thick,  is  of  good  clay,  very  slightly 
moistened,  and  beaten  round  a  hollow  wooden  core,  for 
which  part  of  a  barrel  of  suitable  size  answers  very 
well.  It  is  topped  with  a  course  of  common  brick,  and 
above  these  is  a  flat  iron  ring,  Figure  4,  with  lugs,  which 
may  be  bolted  down,  or  simply  let  in  flush  with  the  top 
of  the  furnace. 

The  grate  bars  are  not  built  in,  but  are  free  to  be 
removed  whenever  desired.  The  furnace  is  constructed, 
when  convenient,  at  the  base  of  the  main  smoke-stack, 
with  which  it  is  connected  by  a  flue ;  otherwise  a  large 
stove-pipe  will  answer  for  a  chimney. 

When  the  weight  of  melted  metal  does  not  exceed 
100  pounds  avoirdupois,  the  pot  is  lifted  out  of  the  fur- 
nace by  hand,  by  means  of  the  basket  tongs,  the  mould 
being  placed  on  the  platform  of  masonry  which  is  seen 
in  the  figure  on  one  side  of,  and  level  with  the  furnace. 
The  melter  stands  on  the  top  of  the  furnace  to  lift,  then 
steps  to  the  ground  one  foot  lower,  to  pour. 


AND    SILVER   BULLION.  17 

If  larger  quantities  of  metal  are  melted  at  once,  a 
lever  may  be  employed  for  lifting  the  pot.  The  lever  is 
arranged  like  that  of  a  blacksmith's  bellows,  being  sup- 
ported by  a  rope,  chain,  or  swivel,  in  such  a  manner  as 
to  admit  of  a  lateral  as  well  as  a  vertical  movement,  and 
at  a  height  of  not  less  than  six  feet  above  the  furnace, 
the  center  of  which  is  directly  under  the  shorter  arm. 

From  the  longer  arm  of  the  lever  a  rope  depends ;  from 
the  shorter  arm  a  link  of  half -inch  iron,  long  enough  to 
reach,  when  drawn  downward,  into  the  cavity  of  the. 
furnace,  and  terminating  in  a  hook  engaging  in  an  eye- 
bolt,  which  forms  the  pivot  connecting  the  jaws  of  the 
tongs. 

The  tongs  being  adjusted  on  the  pot,  a  ring  is  slipped 
over  the  handles  to  hold  them  together ;  the  melter  stead- 
ies them,  while  an  assistant,  pulling  on  the  rope  at  the 
other  end  of  the  lever,  lifts  the  pot  out  of  the  furnace, 
and  swings  it  near  to  the  mould,  when  the  melter  pours 
the  metal. 

The  hands  and  arms  of  the  melter  are  protected  by 
gloves,  which,  in  some  works,  are  elaborately  made  of 
canvas  and  padding.  To  make  a  glove,  I  simply  take 
an  ore  sack,  double  it  lengthwise,  and  sew  it  so  as  to 
form  a  narrow  bag,  of  two  thicknesses  of  canvas,  into 
which  the  arm  may  be  thrust  to  the  shoulder.  The 
gloves  may  be  wetted  to  prevent  burning,  but  hot  arti- 
cles must  not  be  grasped  with  a  wet  glove,  because  the 
steam  produced  will  scald  the  hand;  yet  moisture  is  a 
good  protection  against  radiant  heat,  while  grasping  the 
cool  handles  of  the  tongs. 

In  melting  with'  charcoal,  the  best  result  is  obtained, 


18  ASSAYING  GOLD 

not  by  keeping  the  furnace  full,  but  by  letting  nearly  all 
the  fuel  burn  away  before  refilling.  A  little  practice 
will  enable  the  melter  so  to  manage  that  there  shall  be 
but  little  coal  in  the  furnace  when  the  time  for  pouring 
arrives,  so  that  it  is  not  in  the  way  when  seizing  the  pot 
with  the  basket  tongs.  The  lifting  must  be  performed 
without  delay,  otherwise  the  tongs  may  become  red  hot, 
and  bend.  The  feet  and  legs  of  the  melter  may  be  pro- 
tected by  woolen  armor,  or  by  wetting  the  boots  an(i 
trowsers;  but  melters  and  assayers  must  not  shrink  from 
a  little  scorching. 

If  there  is  much  fuel  left  in  the  furnace  when  the 
melting  i^  ended,  the  grate  is  taken  out,  and  the  embers 
fall  into  the  ash  pit,  where  they  are  extinguished 

Clinkers,  if  formed  on  the  sides  of  the  furnace,  from 
the  melting  of  the  lining,  or  from  dirty  fuel,  are  punched 
ofi",  while  red  hot,  by  means  of  an  iron  bar  with  a  chisel 
end.  If  they  were  to  be  removed  after  coolings  the 
walls  would  be  broken. 

If  making  a  bar  of  clean  skimn-ed  metal,  it  is  proper 
to  throw  a  little  resin,  or  powdered  charcoal  into  the  pot, 
a  few  seconds  before  pouring.  It  prevents  the  sputtering 
which  is  often  caused  by  the  formation  of  base  oxides. 
As  soon  as  such  a  bar  is  cast,  the  top  of  it  is  covered 
with  charcoal  powder,  to  prevent  oxidation  while  solidi- 
fying. When  the  slag  or  matte  is  poured  with  the 
metal  the  charcoal  is  not  required. 

In  a  first-class  office,  the  top  of  the  furnace  consists  of 
a  heavy  plate  of  cast  iron,  sloping  upward  toward  the  flue, 
and  provided  with  sliding  covers.  A  melting  furnace 
should  have  a  strong  draft,  controlled  by  a  damper  in  the 


AND   SILVER   BULLION. 


19 


chimney.  The  flue  connecting  the  furnace  with  the  stack 
or  chimney  should  be  10  inches  or  more  in  width  and 
about  6  inches  high,  in  order  to  admit  of  placing  a  6-inch 
cupel  within  it  for  a  purpose  which  will  appear  hereafter. 
The  floor,  to  a  width  of  4  feet  on  the  front  and  sides 
of  the  furnace  or  set  of  furnaces,  should  be  paved  with 
bricks.  A  furnace  of  which  the  interior  is  16  inches 
square, is  laige  enough  for  the  melting  of  2,000  ounces  of 
silver  at  once. 


Black-Lead  Crucibles. — Made  of 
a  mixture  of  clay  and  plumbago;  used 
for  the  melting  of  bullion  in  the  melt- 
ing furnace;  can  be  used  from  10  to 
20  times. 


No 1         2         3         4  5 

Prices,  each 15c      20c     25c     30c      37c 

Price,  covers,  T  doz $1.50    1.50    1.75    2.25 

No 6         8        10  12 

Prices,  each 40c      50c     55c  60c 

Price,  covers,  T  doz $2.50     2.50  3.00        3.60 

Numbers  14,  16,  18,  20,  25,  30,  35,  40,  45,  50,  60,  70,  80, 

90,  100,  150. 
Price,  per  number,  4  J  cts.    Covers,  price,  per  number,  2  J  cts. 

Tongs. — Straight,  bent,  and  basket  tongs  of  several 
sizes,  adapted  to  the  crucibles.  The  basket  tongs  are 
constructed  to  grasp  the  pot  around  below  the    bulge, 


20  ASSAYING    GOLD 

or  both  above  and  below,  by  curved  arms  attached  to 
the  jaws;  they  are  used  only  for  the  larger  sizes  of  pots, 
say  above  number  20.  Smaller  pots  are  seized  by  the 
rim  with  the  straight  or  crooked  tongs.  Also  bar  tongs 
with  broad,  flat,  and  long  jaws  for  lifting  hot  bars. 
Straight  pokers  for  adjusting^  the  coals,  and  bent  for 
clearing  the  grates  from  below,  are  needed. 

Skimmers. — Iron  rods  3  to  4  feet  or  more  in  length, 
of  :J  to  J  inch  thickness ;  at  one  end  formed  to  a  close 
flat  spiral,  making  a  disc  from  2  to  4  inches  diameter 
at  an  obtuse  angle  to  the  rod,  which  is  suitably  bent  for 
convenient  use  in  removinor  slas:  from  the  surface  of 
molten  metal. 

Gloves. — Made  of  canvas,  with  a  thumb,  but  not 
separate  fingers ;  padded  on  the  back.  Used  to  protect 
the  hands  of  the  melter  from  the  heat.  A  narrow  bag 
of  doubled  sackcloth,  or  blanket  covered  with  canvas, 
intj  which  the  arm  can  be  thrust  to  the  shoulder,  is  as 
good,  and  much  cheaper. 

Stirrers. — Strips  of  the  same  material  as  the  cruci- 
bles. Pieces  sawed  from  the  sides  of  wurnout  pots  an- 
swer.    Used  for  stirrinof  the  molten  metal. 


Bar  Moulds. — Made  of  cast-iron. 
Used  to  pour  the  molten  metal  into 
in  order  to  form  a  bar  or  ingot. 


Ounces,  Silver,  15  20  27  40  52  80  107  112 
Oances,  Gold,  28  35  50  75  107  150  200  207 
Pfica,  eacli,         $.50     .50      .50     .75     1.00     1.25    1.75     2.00 


210 

250 

265 

320 

428 

500 

638- 

388 

400 

495 

600 

800 

921 

1000 

3.25 

3.50 

3.75 

4.00 

4.25 

4.50 

5.00 

AND   SILVER   BULLION.  21 

Ounces,  Silver,  160 
Ounces,  Gold,  300 
Price,  each,         $2.75 

Larger  sizes  can  be  had  up  to  2,000  ounces  of  silver. 

Hammers  and  Chisels. — Round  faced  hammers  for 
smoothing  bars,  and  chipping  hammers  for  driving  the 
chisel,  of  different  sizes,  from  4  ounces  to  4  pounds,  ac- 
cording to  the  bars.     Thin  sharp  cold-chisels  for  chipping. 

Sundries. — A  strong  table  should  stand  near  the 
melting  furnace,  on  which  to  place  the  crude  bullion,  as 
gold-dust,  or  lumps  of  retorted  amalgam,  etc.,  in  sheet- 
iron  pans,  in  readiness  for  melting;  also  to  place  the 
cleaned  bars  on,  etc.  There  should  be  a  rack  in  which 
tongs  and  fire-irons  may  rest,  standing  on  end  on  the 
bricked  floor,  conveniently  for  use.  A  simple  rail  with 
some  nails  projecting  will  serve.  Some  put  the  nails  in 
the  edge  of  the  table  which  then  stands  behind  the  melter, 
who  has  only  to  turn  around  and  put  his  hand  on  what 
he  requires;  also  a  tub  of  water  in  which  to  cool  the 
bars,  with  a  sloping  platform  adjoining,  on  which  to 
clean  them,  arranged  to  drain  into  the  tub;  a  box  of 
sharp  sand  for  scouring  the  bars,  a  scrubbing  brush,  and 
a  tight  roll  of  canvas  about  IJ  inches  thick,  the  wetted 
end  to  be  dipped  in  the  sand  and  applied  to  the  bars  as 
a  scourer.  For  polishing  gold  bars  some  use  a  bundle 
of  brass  wires  as  a  brush.  Diluted  sulphuric  acid,  in 
a  tub  or  vat,  is  sometimes  used  for  "pickling''  a  bar 
containing  base  metal,  to  improve  its  appearance,  and 
a  bottle  of  acid  is  usually  kept  at  hand  for  use  in  the 
scouring.  A  block  of  timber  set  on  end,  the  top  covered 
by  sheet  zinc  and  enclosed  by  a  rim  or  ledge,  is  required 
to  place  bars  on  for  chipping.     Some   small   sheet-iron 


22  ASSAYING   GOLD 

pans  for   samples  {chips   or  dips),  and  larger   ones  for 
crude  metal. 

Stamps. — Letters,  figures,  dollar  sign.  No.,  Oz.,  and 
words,  such  as  Fine,  Value,  Total,  Gold,  Silver,  and  the 
name  of  the  assay er;  made  of  steel  and  used  for  mark- 
ing the  bars.  Sizes,  from  3-2  inch  to  f  inch.  Should  be 
arranged  in  holes  in  a  block  of  wood  for  convenience. 


BULLION    BALANCES    AND     WEIGHTS. 


AND   SILVEK   BULLION.  23 

Becker's  Balance,  100  oz.  to  \i  grain  and  weights $  55.00 

500  *«     "  1        "       "  "        195.00 

♦*  "       2,000  "     "  2        "       "  "         338.00 

Oertling's  London,  200,  300,  1,000,  2,000  ozs. 

Glass  cases  and  supporting  tables  are  supplied,  if  re- 
quired. 

Bullion  Scales. — These  scales,  though  strong  and 
massive,  are  also  delicate,  and  are  provided  with  apparatus 
by  which  the  respective  bearings  are  relieved  when  not  in 
use ;  also  with  an  arrangement  by  which  the  pans  are  stead- 
ied while  the  weights  are  adjusted.  In  using  the  balance, 
the  object  to  be  weighed  and  the  heavier  of  the  neces- 
sary weights  must  be  placed  on  the  pans  before  the  beam 
is  suspended  on  its  bearings  by  a  turn  of  the  crank  in 
front  of  the  base.  The  lighter  weights  for  completing 
the  weighing  are  then  adjusted  while  the  pans  are 
steadied  by  the  arrangement  spoken  of  above,  and  re- 
leased by  a  touch  when  desired.  Scoops  and  pans  for 
gold-dust,  etc.,  accompany  the  scales. 

In  large  establishments,  two  pairs  of  bullion  scales  are 
used,  one  very  massive  pair  for  large  quantities  of  metal 
(chiefly  silver),  and  a  lighter  pair  for  smaller  lots,  espe- 
cially gold.  The  larger  balance  has  only  the  upper  part 
inclosed  in  a  glazed  case ;  the  gold  scales  are  completely 
inclosed.  In  silver  mills,  platform  scales  are  often  used  for 
the  weighing  of  the  bars ;  they  can  be  obtained  to  show 
both  troy  and  avoirdupois  weight,  or  the  latter  may  be 
converted  into  troy  by  calculation,  or  by  means  of  the 
Assay  Table  for  20  grammes  of  ore  in  Part  I. 


24 


ASSAYING   GOLD 


Mattr  ASSES. — Thin 
glass  flasks,  used  for 
parting  bullion  assays, 
and  for  other  purposes. 
Three  ounce,  flat-bot- 
tomed mattr  asses  are 
suitable  for  bullion 
parting. 
$1.50    1.75    2.00 

1        IK       2 

$1.25     1.25     1.50 

%         %         1 


2.25 

2K 
1.75 

VA 


2.50 

3 
2.00 

2 


No.  20.     Round  Bottom,  per  doz 

Capacity  in  oz. 
No.  21.     Flat  Bottom,  per  doz. 

Capacity  in  oz. 

Charred  Lentils. — Made  by  heating  lentils  in  a 
closely  covered  vessel  until  no  fumes  are  given  ofl".  Boil- 
ing acid  is  liable  to  bumping;  this  is  prevented  by  plac- 
ing a  small  piece  of  charcoal  in  the  mattrass.  Common 
charcoal  answers,  but  charred  lentils  throw  off*  no  frag- 
ments. -' 

Hydrometer. — A  floating  gauge,  made  of  glass  and 
loaded  with  shot  at  the  lower  end.  Placed  in  a  liquid 
it  floats  in  a  vertical  position,  a  greater  or  less 
portion  of  the  graduated  stem  being  submerged 
according  to  the  density  of  the  liquid ;  used  as  a 
measure  of  the  density,  and  therefore  the 
strength,  of  acids,  etc.  There  are  several  kinds 
of  hydrometers;  that  of  Baume  is  generally 
used  in  assay  offices.  In  ordering  a  hydrometer, 
state  the  pui-pose  for  which  it  is  required,  be- 
cause some  are  arranged  for  liquids  lighter  than 
^  water.  These  would  not  answer  for  acids.  It 
is  best  to  procure  one  which  is  graduated  to 
show  specific  gravity  as  well  as  degrees  Baume, 
because  the  strength  of  the  acid  is  indicated  in 
either  in  the  books.     Price,  75  cents. 


AND   SILVER   BULLION. 


25 


Cats 

Ct;Mtr 


Graduated  Cylinder. — The  hydrometer 
is  used  in  a  narrow  glass  vessel,  which  need 
not  be  graduated  for  this  purpose,  but  a  grad- 
uated vessel  is  useful,  and  it  answers  equally 
for  floating  the  hydrometer.  As  to  the  grad- 
uation, grammes  and  c.  c.  are  the  same,  a 
gramme  being  the  weight  of  a  -«.  c.  of  pure 
water  at  standard  temperature. 


Contents  in  cubic  cent 

Open  top  with  spout,  price,  each 

With  Glass  Stoppers 

Contents  in  cubic  cent... 

Open  top  with  spout,  price,  each 
With  Glass  Stoppers,  price,  each 
With  spout  reading  upwards  } 
graduated  into  grammes,    ^' 


50  75 

100 

65  .75 

1.00 

.90  1.00 

1.25 

500 

1,000 

2.00 

3.00 

2.25 

3.50 

0   100 

200 

5  1.00 

1.25 

5     10    25 
$0.30  .40  .50 
$0.75 
250 
$1.25 
$1.62 

10      20      5 

iiiiu  giauiiues,      ) 

Price,  each $0.30    .40     .50     .7 

Beakers. — Thin  glass  jars,  which 
will  bear  rather  rapid  change  of  tem- 
perature without  fracture.  Used  in 
treating  substances  with  acids,  etc., 
and  for  receiving  the  liquid  from  a 
filter  (filtrate).  Not  essential  in  the 
ordinary  routine  of  assaying  gold  and 
silver,  but  very  appropriate  in  an 
office,  and  requisite  in  the  assays  of 

copper  and  other  base  metals. 

Nest  of 3  5  6  8  10 

Price  each  nest,  plain $0.38     .75       1.25     1.60        3.00 

with  lip $1.00     1.50    2.00         3.12 

3 


26 


ASSAYING   GOLD 


SINGLE   BEAKERS— PLAIN. 

In  depth,  inches 10        8        6        6     5^   4^^      4        3 

In  width,  inches 6         5        5        4       4      33^    23^      2 

Price,  each -. $1.00     .90     .80     .60     .50     .40     .25     .15 

Evaporating  Dishes.— Made  of  glazed 

porcelain.      Will  withstand  heat  and  acids ; 

used  for  dissolving  and  drying ;  not  essential 

in  assaying  gold  and  silver. 

No ..-       00       01234  5         67 

Capacity,  oz.        2  4       8      16      24     1  qt.  3  pt.  ^  gal.  %  g. 

Diameter,  in.      33^      4.%    6%   6^     7^      8%       10       11      12 
Price $0.30     .35     .40     .60    1.00     1.25     1.35     150    1.80 


\*i»ffiaA*, 


CoAL-uiL  Stove.  —  Useful 
anywhere.  Almost  indispen- 
sable in  a  country  office  where 
gas  cannot  be  had.  A  sheet- 
iron  dish  containing  some 
sand,  placed  on  the  stove, 
forms  a  sand-bath  convenient 
for  the  parting. 

each .  - $1.75 

3.20 

4.20 

5.30 

6.50 

Flatting  Mill  (Rolling  Mill). — A  pair  of  steel  rollers, 
with  adjusting  screws  and  cranks  to  operate  by  hand. 
Used  in  laminating  metal;  can  be  dispensed  with,  but 
not  conveniently,  by  using  the  hammer  and  anvil  instead- 
Prices,  fromS35.00  to  S65.0().  Other  apparatus  will  be 
mentioned  in  the  course  of  description  of  methods. 


AND   SILVER   BULLION.  27 


MELTING  BULLION. 


The  fuel  used  is  coke  or  charcoal,  or  in  some  places, 
stone  coal.  It  should  be  screened  free  from  dust  and 
dirt.  Lumps  larger  than  a  turkey's  egg  should  be 
broken.  When  coke  is  used,  a  little  charcoal  is  necessary 
to  start  with. 

New  black-lead  pots  must  be  annealed.  To  anneal  a 
pot  and  cover,  kindle  a  fire  in  the  furnace,  and  invert 
the  pot  over  the  fire;  put  the  cover  also  in  the  furnace; 
add  fuel,  check  the  draft,  and  increase  the  heat  very 
gradually  until  the  pot  and  cover  are  red-hot.  They  are 
then  ready  for  use,  and  may  thereafter  be  placed,  even 
when  cold,  in  the  hottest  fire  without  danger  of  fracture. 

The  metal  to  be  melted,  if  in  small  quantity,  is  put 
into  the  cold  (annealed)  pot  as  it  stands  on  the  table,  or 
on  the  furnace  plate ;  the  pot  is  then  placed  in  the  fire, 
renting  on  a  piece  of  fire-brick.  Otherwise  the  pot  is 
put  into  the  fire  first,  and  large  bars  or  lumps  are  placed 
within  it  by  means  of  tongs,  gold-dust  or  small  frag- 
ments of  metal  by  means  of  a  scoop  and  sheet-iron  fun- 
nel. Borax  is  added,  the  pot  covered,  and  fuel  placed 
around  and  above  it.  Retorted  amalgam,  especially  sil- 
ver, is  porous  and  bulky;  hence  the  pot  must  be  refilled 
from  time  to  time  as  the  metal  subsides,  and  as  such 
metal  contains  some  quicksilver,  the  addition  should  bo 


28  ASSAYING   GOLD 

made  before  that  in  the  pot  is  quite  melted,  while  it  is  in 
a  pasty  condition,  otherwise  spirting  may  occur.  The 
melter  should  be  careful  not  to  inhale  the  fumes. 

When  the  metal  and  the  slag  formed  by  the  borax 
with  the  impurities  are  melted,  the  latter  must  be  re- 
moved. The  skimmer  is  placed  in  contact  with  the  slag, 
of  which  a  portion  adheres;  the  skimmer  is  then  with- 
drawn, pressed  on  the  furnace  plate  previously  greased, 
or  on  any  suitable  surface,  to  chill  and  flatten  the  adher- 
ing slag,  dipped  slightly  in  cold  water  to  further  cool  it, 
and  again  touched  to  the  slag.  If  the  slag  is  in  such 
quantity  as  to  accumulate  inconveniently  on  the  skim- 
mer, it  is  thoroughly  cooled  in  water  and  knocked  off 
by  a  blow  with  the  hammer.  Toward  the  end,  however, 
it  is  better  if  the  skimmer  is  not  cleaned,  because  the 
metal  is  less  liable  to  adhere  to  a  surface  of  slag  than  to 
the  naked  iron. 

The  slag  must  be  of  medium  consistency,  neither  pasty 
nor  too  liquid.  If  pasty,  it  may  retain  considerable 
globules  of  metal;  if  too  thin,  it  cannot  be  readily 
skimmed  off.  A  thick  slag  may  be  thinned  by  an  addi. 
tion  of  borax;  or  if  sand  be  the  cause,  a  little  soda  may 
be  employed ;  but  as  soda  attacks  the  pot,  it  must  be 
used  with  care.  A  thin  slag  may  be  thickened  by  means 
of  sand. 

When  all  slag  has  been  removed,  if  the  surface  of  the 
metal  is  bright  it  is  ready  for  pouring.  If  it  is  covered 
by  a  scum  or  crust,  it  probably  contains  copper  or  iron, 
perhaps  also  sulphur.  If  rainbow  colored  rings  appear, 
lead  is  most  likely  present  in  small  quantity,  and  more 
if  brilliant  spots  appear  moving  rapidly. 


AND   SILVER   BULLION.  29 

In  the  first  case,  some  lumps  of  borax  are  to  be  thrown 
on  the  metal  and  allowed  to  melt,  absorbing  the  base 
oxides  and  forming  a  slag  which  must  be  removed  as 
before.  If  this  does  not  seem  to  be  efficacious,  sulphur 
is  probably  present,  and  a  little  nitre  may  be  added  to 
the  borax,  or  better  a  mixture  of  nitre  and  glass  powder. 
If  much  copper  or  iron  is  present,  it  is  best  to  add  a  little 
lead  to  the  metal  in  the  pot;  the  colored  rings  or  bright 
spots  then  appear,  being  produced  by  the  formation  of 
litharge,  which  rapidly  oxidizes  the  copper  and  iron, 
forming  slag.  As  the  plumbago  of  the  pot  is  a  reducer 
(Part  I,  page  33),  it  constantly  tends  to  the  reconversion 
of  the  litharge  to  lead,  and  of  other  oxides  to  the  respect- 
ive metals,  while  litharge,  being  a  flux  for  all  earthy 
matters,  attacks  also  the  clay  of  the  pot.  To  prevent 
this  reverse  action  and  protect  the  pot,  some  cupels  are 
introduced  which  float  on  the  liquid  metal  and  absorb 
the  litharge,  etc.  The  cupels  are  removed  when  saturated. 
Unless  the  bullion  is  very  nearly  all  precious  metal,  the 
refining  by  these  methods  is  too  tedious,  but  sulphur 
should  be  removed  in  order  to  make  a  bar  which  can  be 
correctly  assayed. 

While  the  melting  is  in  progress,  a  stirrer  is  heated  to 
redness,  and  a  suitably  sized  mould  is  warmed.  To  pre- 
vent adherence  of  the  metal,  a  mould  for  a  gold  bar  is 
smoked  by  being  placed  in  a  small  chamber,  or  mounted 
on  two  brickbats,  over  a  dish  of  burning  resin,  or  a  quite 
small  mould,  by  holding  it  over  the  flame  of  a  lamp.  It 
is  thus  warmed  at  the  same  time.  For  a  silver  bar  of 
any  considerable  size,  greasing  is  usually  preferred;  or 
the  mould  may  be  painted  with  a  wash  of  finely  sifted 
ashes  and  water;  then  thoroughly  dried  and  warmed. 


30  ASSAYING   GOLD 

After  the  skimming,  the  metal  in  the  pot  is  covered 
by  a  layer  of  charcoal  powder,  and  left  for  a  few  min- 
utes, the  pot  being  covered.  This  reduces  any  base 
metal  oxide  that  may  have  formed,  and  which  would 
cause  the  metal  to  sputter  when  poured,  or  it  prevents 
the  sprouting  of  nearly  pure  silver.  A  silver,  doree,  or 
base  silver  bar,  if  of  considerable  size,  must  now  be  sam- 
pled (all  very  small  bars  are  chipped).  The  pot  is  taken 
from  the  fire,  placed  on  the  furnace  top,  and  the  metal 
stirred  by  an  assistant,  with  the  heated  stirrer  held  in 
the  tongs,  while  the  melter  dips  out  two  separate  sam- 
ples of  30  to  50  grains  each,  and  pours  them,  from  a 
height  of  a  foot  or  two,  into  dishes  of  water,  by  which 
the  metal  is  granulated.  The  dipping  is  usually  done 
with  a  very  small  crucible,  hessian  or  french,  heated 
to  redness  and  held  in  a  pair  of  tongs.  A  heated  rod 
of  iron  is  often  used  for  the  stirring,  and,  if  the  end  is 
formed  into  a  small  ladle,  for  the  dipping  also;  an  as- 
sistant is  not  then  required.  The  metal  is  then  poured 
into  the  bar-mould,  the  charcoal  being  held  back,  if  nec- 
essary, by  means  of  an  iron,  such  as  the  bent  poker, 
until  nearly  all  the  metal  has  run  out.  Some  more  char- 
coal dust  is  then  thrown  on  the  bar  to  keep  the  surface 
covered;  or,  if  the  bar  is  small,  some  oil  may  be  poured 
on  it.  The  purpose  is  to  prevent  oxidation.  The  slight 
cooling  of  the  metal  during  the  stirring  and  sampling 
does  no  harm,  for,  if  silver  is  poured  too  hot,  the  face 
of  the  bar  will  be  spongy.  The  gianulated  samples,  or 
"  dips,"  are  dried,  and  are  then  leady  for  the  assay er. 
A  gold  bar  is  poured  as  soon  as  melted  and  stirred,  the 
samples  not  being  taken  by  dipping. 

In  the  melting  rooms  of  Professor  Price,  in  San  Fran- 


AND   SILVER   BULLION.  31 

cisco,  the  heaviest  bars  are  cast  without  the  use  of  a 
crane  or  of  basket  tongs.  Two  men  grasp  the  pot  on 
opposite  sides  by  means  of  straight  ''side  tongs,"  the 
jaws  of  which  are  formed  to  suit  the  thickness  of  the 
pot,  so  as  not  to  bite  a  piece  out,  and  it  is  lifted  out  of 
the  furnace  in  less  tiii:e  than  would  be  required  to  adjust 
the  basket  tongs.  The  pot  is  tilted  for  the  pouring  by 
means  of  a  pair  of  tongs,  which  are  held  in  a  horizontal 
position,  having  semi-circular  jaws  grasping  the  pot 
about  the  middle.  This  way  of  pouring  requires  con- 
siderable strength,  and  the  basket  tongs,  suspended  from 
a  crane  by  means  of  an  eye  formed  on  the  pivot  of  the 
tongs,  and  having  the  liandles  secured  by  a  ring  slipped 
over  them,  seem  preferable  for  heavy  work.  At  Los 
Bronces,  in  Mexico,  the  furnace  was  deeply  set  in  the 
ground,  the  ash-pit  covered  by  an  iron  grating  on  which 
the  workmen  stood.  The  pot  contained  enough  metal 
for  a  number  of  bars.  It  was  lifted  by  a  crane,  and 
placed  in  a  carrier,  such  as  is  used  by  founders  for  car- 
rying melted  iron  to  the  flasks,  and  two  men  lifted  it 
and  filled  the  moulds  in  succession. 

When  the  bar  is  solid,  it  is  turned  out  of  the  mould 
by  upsetting  that,  cooled  in  water,  any  slag  beaten  off*, 
scoured,  smoothed  if  necessary  by  hammering,  and 
dried.  A  bar  which  has  been  sampled  by  dipping  is 
now  ready  for  weighing,  otherwise  it  must  first  be 
chipped.  The  chips  are  taken  from  two  diagonally  op- 
posite corners,  one  top  and  one  bottom.  The  chisel  is 
held  between  the  thumb  and  forefinger  of  the  left  hand, 
while  the  remaining  fingers  of  that  hand  retain  the 
chips  which  would  otherwise  be  projected  to  a  distance. 
The  chips  are  taken  in  many  small  pieces,  to  facilitate 


32 


ASSAYING   GOLD 


the  weighing  of  the  assay,  and  each  sample  is  placed  on 
a  separate  piece  of  paper,  one  corner  of  which  is  bent 
up  for  convenient  handling.  The  number  of  the  deposit 
is  marked  on  the  paper.  One  assay  is  made  from  each 
sample,  and  if  the  two  do  not  agree,  and  a  "control" 
assay  fails  to  correct  the  discrepancy,  the  bar  is  remelted 
and  better  mixed.  The  samples  should  be  large  enough 
to  allow  of  several  assays  being  made  of  each,  and  any 
residue  is  folded  in  the  paper,  the  number  being  left 
visible,  and  kept  for  future  reference  in  case  of  need. 
The  chipped  corners  of  the  bar  are  neatly  dressed  by 
the  hammer,  and  impressed  with  a  stamp,  as  a  security 
against  being  tampered  with.  The  bar  is  then  weighed, 
and  a  tag  bearing  the  number  and  weight  pasted  on,  to 
remain  until  the  stamping;  or  the  number  and  weight 
may  be  stamped  at  once. 

Each  bar  is  finally  stamped  on  the  face,  which  is  that 
side  which  was  the  bottom  when  cast,  with  the  name 
and  address  of  the  assay er,  the  weight  in  troy  ounces 
and  hundredths,  and  the  fineness  and  value  in  gold,  or 
in  both  gold  and  silver,  according  to  the  character  of  the 
bullion,  as  explained  above.     On  delivery  it^  is   accom- 


panied by  a  certif- 
icate, stating  the 
number  of  the  de- 
posit, the  name  of 
the  depositor,  the 
weight  before  and 
after  meltinef,  and 
all  other  partic- 
ulars as  stamped ; 


C.  H.  AARON, 

I 

ASSAYER. 

No 1754 

Oz 172.54 

Fine  Gold.    .978 
Value,  $3,488.24 


also  the  charges 
for  melting  and 
assaying,  against 
which  is  offset 
the  value  of  the 
chips  and  grains. 
The  chips  are 
the  samples;  the 
grains    are     any 


glolules  of   metal  which  may  remain   in  the  pot  after 


AND    SILVER   BULLION.  33 

pouring,  or  which  may  be  removed  with  the  slag  in  the 
skimming,  all  of  which  must  be  collected,  cleaned,  and 
weighed.  A  convenient  way  in  which  to  arrive  at  the 
weight  of  the  chips  and  grains  is  to  weigh  the  bar  and 
grains  together  before  chipping,  then  chip,  and  weigh 
the  bar  alone  for  its  delivery  weight.  The  difference  is 
the  weight  of  chips  and  grains,  the  value  of  which  is 
reckoned  according  to  the  result  of  the  assay.  The 
value  stamped  on  a  bar  is  the  assay  value.  The  com- 
mercial value  depends  on  the  state  of  the  market  for  the 
particular  description  of  bullion. 

Gold  is  frequently  purified  from  base  metal  in  the  fol- 
lowing manner :  The  melted  metal  is  slowly  poured  from 
a  height  of  several  feet  into  a  vessel  containing  water, 
which  is  meanwhile  agitated  by  means  of  a  stick.  The 
metal  is  thus  granulated.  It  is  then  dried  and  remelted 
with  addition  of  nitre  and  borax.  The  melting  with 
nitre  must  not  be  done  in  a  black-lead  pot,  but  in  a 
"sand-pot,"  or  one  of  clay.  The  nitre  in  decomposing 
leaves  caustic  potassa  which  violently  attacks  the  pot, 
as  do  also  the  base  metal  oxides  formed.  This  may 
easily  lead  to  fracture,  when  the  spilled  metal  must  be 
recovered,  as  far  as  possible,  by  washing  the  ashes  and 
cinders,  after  allowing  the  fire  to  burn  out.  To  prevent 
such  an  accident,  two  devices  are  employed.  Firstly, 
a  dish,  made  by  cutting  down  a  wornout  black-lead  pot, 
is  placed  under  the  sand-pot  in  the  furnace,  as  a  saucer 
under  a  cup.  This  receives  the  metal  in  case  oE  a  break. 
Secondly,  a  quantity  of  clean  quartz  sand,  equal  to 
about  half  the  bulk  of  ^  the  nitre,  is  mixed  with  that  and 
the   granulated   metal.     The    sand    combines   with   the 


34  ASSAYING   GOLD 

metal  oxides  and  the  potassa,  forming  a  liquid  slag  or 
glass.  Without  this  addition  of  sand,  iron  or  copper 
oxide  would  not  become  liquid  unless  a  large  proportion 
of  borax  were  used.  The  metal  and  slag  are  poured 
together  into  a  mould.  Sometimes  a  very  neat  bar  is 
thus  made,  which  does  not  require  remelting,  but  fre- 
quently the  slag  gets  between  the  metal  and  the  mould, 
spoiling  the  appearance  of  the  bar,  and  making  it  dif- 
ficult to  clean.  In  this  case  the  bar  is  remelted.  with  a 
little  borax  in  a  black-lead  pot.  If,  however,  it  is  not 
pure  enough,  the  granulation  and  melting  with  nitre  are 
repeated.  Retorted  amalgam  does  not  require  granu- 
lation, being  porous  enough  for  the  melting  nitre  to  per- 
meate it. 

The  fusion  with  nitre  must  be  done  carefully  and 
under  a  very  low  heat  for  some  time ;  otherwise  the  con- 
tents of  the  pot  will  overflow.  The  pot  should  not  be 
more  than  half  filled  with  the  mixture.  It  is  not  safe  to 
attempt  a  second  use  of  the  saud-pot,  as  it  is  almost  cer- 
tain to  break. 

A  very  good  way  in  which  to  purify  small  lots  of  gold 
or  silver  containing  base  metal  is  by  cupellation.  A  worn 
out  black-lead  pot  is  cut  down  so  as  to  form  a  dish  from 
2  to  4  inches  deep  in  which  a  cupel  is  made  by  beating  in 
moistened  bone  ashes,  and  scooping  a  hollow  in  the  top. 
The  cupel  is  well  dried  in  the  dish,  which  may  have  some 
holes  drilled  through  it  with  advantage.  When  required 
for  use,  it  is  placed  in  the  flue  of  the  melting  furnace 
while  the  fire  is  in  use  for  other  purposes.  As  soon  as 
the  cup?!  is  red  hot,  some  lead  is  placed  on  it,  and  when 
that  is  melted  the  impure  gold  or  silver  is  added  and 


AND    SILVER   BULLION.  35 

cupelled  without  expenditure  of  time  or  much  fuel,  be- 
cause the  melting  of  other  lots  may  be  going  on  in  the 
furnace.  The  furnace  must  be  left  a  little  open  to  admit 
air  for  the  cupellation. 

A  few  ounces  of  metal  may  be  cupelled  in  the  or- 
dinary muffle,  a  cupel  being  made  in  the  following  man- 
ner: a  strip  of  cotton  cloth  is  laid  across  a  small  bar- 
mould,  and  pressed  down  into  it,  the  ends  of  the  cloth 
projecting.  Moist  bone  ashes  are  then  beaten  in  until 
the  mould  is  full.  A  depression  is  formed  in  the  top  by 
means  of  a  knife,  and  smoothed  by  the  bowl  of  a  spoon. 
The  cupel  is  then  lifted  out  of  the  mould  by  means  of 
the  strip  of  cloth  which  passes  under  it,  and  dried. 

Refining  as  described  does  not  remove  silver  from  gold 
bullion.  In  Australia,  silver  and  copper  are  removed 
from  gold  by  injecting  chlorine  through  a  clay  tube  (pipe 
stem)  plunged  into  the  melted  metal.  The  chlorine  com- 
bines with  the  copper  and  silver ;  the  copper  chloride  vola- 
tilizes; the  silver  chloride  floats  on  the  gold  and  is  poured 
off  as  soon  as  the  gold  solidifies  by  cooling,  after  which 
the  gold  is  again  heated  to  melting  and  cast  in  a  mould. 


36  ASSAYING   GOLD 


ASSAYING  BULLION 


In  ore  assaying  (Part  I)  the  weight  of  precious  metal 
obtained  is  usually  stated  in  thousandth  parts  of  a 
fiframme,  of  a  half  oframme,  or  of  ten  grains,  regarded 
as  integers  and  so  written,  to  which  I  have  given  the 
name  of  "points,"  a  term  borrowed  from  the  bullion 
assay,  and  more  suitable  than  "  thousandth,"  which  ex- 
presses a  fraction.  In  bullion  assaying,  unfortunately, 
nomenclature  and  notation  are  not  quite  consistent.  The 
object  of  the  assay  is,  to  find  out  how  many  parts  in  one 
thousand  equal  parts  by  weight  of  the  bullion  consist  of 
pure  gold  or  silver;  or,  which  amounts  to  the  same, 
mathematically,  how  many  .001  of  1  part  are  gold  or 
silver.  In  writing,  and  in  stamping  the  bar,  the  latter 
view  is  taken,  and  we  use  the  decimal  mark  thus,  fine 
gold  .572;  fine  silver  .422;  that  is,  so  many  thousandths 
of  a  part  in  one  part  of  the  alloy.  But  in  speaking  we 
say,  the  bullion  is  so  many  fine  in  gold  or  silver,  not  men- 
tioning thousandths,  but  implying  so  many  parts  (units) 
in  a  thousand.  The  mathematical  value  of  the  two 
modes  of  expression  is  identical.  Moreover  in  speaking 
the  thousandths  are  often  called  "points,"  as,  "this  bar 
is  four  points  finer  than  that,"  or,  "add  three  points  for 
cupellation  loss." 

To  show  the  difference  between  the  reporting  of  an  ore 
assay  and  that  of  a  bar;  supposing  the  gramme  weights  to 


AND    SILVER    BULLION.  37 

be  used,  0.065  gramme,  or  65  milligrammes  of  gold,  if 
got  from  an  ore  assay  would  be  written  (and  called)  65, 
but  if  from  an  assay  of  bullion  would  be  written  .065; 
the  bar  would  be  stamped,  fine  gold  .065 ;  but  in  speak- 
ing of  it  we  should  say,  "  It  is  sixty -five  fine,"  adding, 
"in  gold,"  if  that  was  not  already  understood.  In  either 
case  it  would  be  meant  that  one  thousand  parts,  of  what- 
ever denomination,  consisted  of  sixty -five  parts  gold  and 
nine  hundred  and   thirty -five   parts   some  other  metal. 

From  this  it  will  be  seen  that  either  of  the  systems  of 
weights  used  in  ore  assaying  will  answer  for  bullion  also, 
or  indeed  any  set  of  weights  decimally  divided  down  to 
one-thousan  dth  of  the  greater  weight,  and  it  matters  not 
whether  the  greater  weight  be  regarded  as  the  unit,  and 
the  lesser  as  a  fraction  of  that,  or  the  lesser  be  considered 
the  unit,  and  the  greater  as  one  thousand  of  such. 

P'or  gold  bars,  using  a  delicate  balance,  half  a  gramme 
is  generally  taken  for  the  assay,  the  purified  metal  being 
weighed  in  half  milligrammes.  With  an  inferior  balance, 
or  for  a  silver  bar,  one  gramme  or  ten  grains  are  the, 
usual  quantities.  Whatever  it  be,  the  weight  taken  is 
called  a  thousand,  whereas,  to  be  consistent  with  the  writ- 
ten expression,  it  should  be  called  one,  and  the  thousandth 
part  of  it,  which  to  agree  with  the  term  thousand  ought 
to  be  called  one,  is  called  a  thousandth,  or  a  point,  which 
is  better.  Hereafter  in  these  pages,  we  shall  speak  of 
thousands  and  points,  discarding  the  awkward  word 
thousandth  entirely. 

In  bullion  assaying,  all  the  weighing,  except  that  of 
the  lead  used,  is  done  on  the  assay  balance.  . 

Gold  Bar. — Natural   gold  is   never  pure.     It  is  al- 


38  ASSAYING   GOLD 

loyed  almost  invariably  with  silver,  frequently  with  cop- 
per, and  the  bars  often  contain  platinum  and  iridium 
which  occur  in  grains  with  the  placer  gold,  lead,  from 
bullets  scattered  about  the  gravel  washings,  and  quartz- 
mill  gold  sometimes  contains  iron  from  the  abrasion  of 
stamps.  All  base  metal  can  be  removed  by  cupellation 
with  lead;  silver  and  platinum,  by  nitric  acid;  for,  al- 
though pure  platinum  is  not  attacked  by  nitric  acid,  it 
dissolves  in  that  when  alloyed  with  two  parts  of  silver; 
and  as  gold  must  also  be  alloyed  with  at  least  twice  its 
weight  of  silver,  in  order  that  the  parting  may  be  com- 
plete, it  will  be  readily  seen  that  the  presence  of  plati- 
num offers  no  serious  difficulty.  Iridium  does  not  melt 
to  an  alloy  with  tha  goLl,  but  remainj^  in  the  form  of 
scales  or  grains. 

It  will  be  remembered  that,  while  two  parts  of  silver 
to  one  of  gold  are  indispensable  to  a  successful  parting, 
more  than  three  parts  would  cause  inconvenience  by  the 
crumbling  of  the  goM.  Moreover,  it  has  been  ascertained 
that,  with  more  than  three  parts,  the  separation  is  less 
perfect  than  with  two  and  a  half  parts,  until  the  propor- 
tion of  eight  parts  of  silver  to  one  of  gold  is  reached, 
when  the  gold  falls  to  absolute  powder  and  remains 
pure. 

The  assayer  endeavors  to  obtain  an  alloy  for  the  part- 
ing, in  which  the  proportion  of  silver  to  that  of  gold 
shall  be  about  two  and  a  half  to  one,  supposing  platinum 
to  be  absent.  A  practiced  assayer  can  usually  judge  from 
the  appearance  of  the  sample,  or  from  former  experience 
with  gold  from  the  same  local it}^,  how  great  a  proportion 
of  silver   it   already    contains,    and,    consequently,    how 


AND   SILVER   BULL  ION  39 

much  must  be  added;  otherwise  a  preliminary  assay  may 
be  made  with  addition  of  so  much  silver  as  to  assure 
the  success  of  the  parting,  even  though  the  gold  may 
crumble,  and  thus  the  requisite  information  be  obtained. 

Preliminary  Assay  of  Gold  Bar. — One  thousand  of 
the  sample  and  four  thousand  of  test  silver  are  enveloped 
in  three  or  four  thousand  of  sheet-lead,  and  cupelled  under 
a  rather  high  heat.  The  bead  is  cleaned,  beaten  by  ham- 
mer and  anvil  to  a  flat  plate,  annealed  by  heating 
to  redness,  parted,  cupped,  dried,  and  weighed,  as  in  ore 
assaying,  but  a  mattrass  is  used  for  the  parting,  instead 
of  a  test-tube,  on  account  of  the  larger  quantity  of 
metal.  The  weight  in  points  is  the  approximate  fineness 
from  which  the  weight  of  silver  required  in  the  proper 
assay  is  known  by  multiplying  by  2.5.*  From  this  the 
quantit}^  already  alloyed  with  the  gold  must  be  deducted, 
in  order  to  ascertain  how  much  must  be  added.  For  ex- 
ample, if  the  gold  got  from  1,000  of  the  sample  weighs 
924,  the  lost  weight  is  that  of  the  silver,  except,  perhaps, 
a  veiy  small  quantity  of  base  metal,  which  need  not  be 
notice<l  in  this  class  of  bullion.  The  bullion  tKen 
contains  924  of  gold,  and  76  of  silver  in  1,000.  Multi- 
plying 924  by  2.5,  we  have  2,310  of  silver  required  for 
the  parting,  of  which  quantity  the  bullion  already  con- 
tains 76,  leaving  2,234  to  be  added. 

Assay  Proper  of  Gold  Bar. — One  thousand  of  the 
sample  is  cupelled  with  such  a  quantity  of  test  silver  as  is 
necessary,  about  3  i  oints  of  copper  and  about  3,000  of  sheet- 

*In  the  case  of  very  small  bars,  this  assay  will  suffice,  if  the  gold  be 
twice  boiled  ia  acid,  well  washed,  cupped  with  care,  and  at  least  two 
points  deducted  from  the  result  found. 


40  ASSAYING  GOLD 

lead,  rolled  into  a  capsule  or  "  cornet"  (Part  I,  page  76), 
and  closely  folded  about  the  assay.  The  lead  cornets  are 
usually  kept  at  hand,  ready  made.  The  weighed  assay 
is  transferred  directly  into  the  cornet,  held  in  the  left 
hand,  from  the  weighing  capsule  which  is  lifted  from  the 
scale  pan  with  the  pincettes.  It  is  not  usual  to  weigh  the 
silver  for  the  inquartation.  A  quantity  of  sheet  silver 
is  cut  into  pieces  of  nearly  known  weight,  and  the  re- 
quired number  of  pieces,  as  well  as  the  copper,  added  to 
the  gold  in  the  lead  cornet,  which  is  folded  in  the  form 
of  a  snug  packet,  and  placed  on  a  watch-glass,  or  in  a 
dry  cup,  which  occupies  its  appropriate  place  on  a  tray 
according  to  the  set  number  of  the  assay. 

As  many  as  14  assays  may  be  thus  prepared  and  cu- 
pelled at  one  time  in  a  mint  muffle.  The  cupels  are 
heated  to  light  redness,  and  the  a&says  are  placed  on 
them  in  regular  order,  according  to  their  respective  num- 
bers in  the  set.  The  muffle  is  then  closed  until  the  as- 
says uncover,  when  the  door  is  left  open.  If  there  is  any 
difficulty  in  keeping  the  front  cupels  hot  enough,  some 
glowing  coals  may  be  placed  in  the  mouth  of  the  muffle. 
It  sometimes  happens,  in  cupelling  a  number  of  assays, 
that  the  uncovering  c)f  one  or  more  is  delayed  by  some 
cause;  a  small  wad  of  folded  paper,  placed  on  the  refrac- 
tory assay  will  set  it  working.  A  strong  heat  is  main- 
tained throughout  the  operation,  and  especially  at  the 
time  of  brightening,  that  is  to  say,  a  higher  desfree  than 
is  admissible  in  a  silver  assay,  because  gold  is  less  vola- 
tile than  silver. 

^  It  is  not  necessary  to  remove  a  gold  assay  the  instant 
the  cupeliation  is  finished,  so  that  all  may  remain  in  the 


AND   SILVER   BULLION.  41 

muffle  until  all  ar6  finished,  and  may  then  be  taken  out 
without '  much  precaution  as  to  cooling,  as  these  assays 
are  not  very  liable  to  sprouting;  the  addition  of  copper 
is  partly  for  the  purpose  of  preventing  the  sprouting,  for, 
notwithstanding  the  cupellation,  a  trace  of  it  remains 
in  the  bead.  Another  reason  for  the  addition  of  copper 
is  that  it  renders  the  metal  tougher  for  the  lamination. 
If,  for  want  of  heat,  an  assay  should  freeze,  or  solidify, 
during  the  cupellation,  it  may  be  refused  by  placing 
glowing  coals  about  the  cupel  and  one  upon  the  top  of 
it;  but  the  assay  is  not  quite  reliable. 

The  cupelled  bead  is  cleaned,  beaten  to  the  forrd'of  a 
bar  about   one-quarter  inch  wide  and  one-eighth   thick, 
annealed    by   heating   to    dull    redness    in    the    muffle, 
and  passed  through  the  flatting  mill  until  it  is  reduced  to 
a  strip  about  as  thin  as  an  ordinary  card.     The   metal 
must  be  annealed  whenever  it  shows  signs  of  cracking  on 
the  edges,  or  becomes  hard  and  elastic  from  the  rolling, 
and  asrain  after  the  rollinor  is  finished.     It  is  then  formed 
into  an  open  coil*  by  the  thumb  and  finger,  placed  in  a 
three-ounce  mattrass  and  gently  boiled  in  one  and   a  half 
ounce  of   nitric  acid  of   32°  Baume,  adding   a  charred 
lentil,  or  a  bit  of  charcoal  to  prevent  bumping.     After 
thus  boiling  for  10  minutes,  the  acid  is  poured  off',  re- 
placed by  a  f i-esh  qu  ntity,  and  the  boiling  repeated  for 
15    or    20    minutes.       It   is   in  the  second  boiling  that 
the  charcoal    is   especially  necessary,  as   there   is    more 
danger  of  the  bumping  of  the  acid  when  the  evolution  of 
gas  ceases. 

The  acid  is  now  again  poured   off",  and  this   time  the 
charcoal  must  go  with  it,  or,  on  the  addition  of   water,  it 

*The  name  of  "  cornet  "  is  given  to  this  as  well  as  to  the  lead  capsule. 

4 


42  ASSAYING   GOLD 

will  sink  and  give  trouble ;  the  gold  is  washed  three  times 
with  hot  water,  cupped,  heated  to  redness  in  the  muffle, 
cooled,  and  weighed.  It  should  be  in  one  piece,  which, 
dark  colored  and  fragile  after  the  parting,  assumes  the 
golden  hue  and  a  fair  degree  of  tenacity  when  heated. 
The  color,  although  golden,  is  liable  to  considerable  varia- 
tions of  shade. 

The  weight  of  the  gold  in  points,  less  from  half  a  point 
to  one  or  two  points  allowed  for  a  small  portion  of  silver 
which  remains  in  it  and  is  called  the  surcharge,^  is  the 
gold  fineness  of  the  bullion,  which  is  stamped  on  the  bar. 
The  results  of  two  assays  should  agree  within  a  quarter 
point  in  weight. 

DoreeBar. — The  assay  is  conducted,  speaking  gener- 
ally, in  a  similar  manner  to  that  of  a  gold  bar.  A  pre- 
liminary is  more  often  necessary  in  this  case,  and  accord- 
ing to  its  indications  either  gold  or  silver  may  be  added  so 
as  to  produce  a  suitable  alloy  for  the  parting.  If  gold 
is  required,  it  is  taken  from  the  cornets  of  previous  as- 
says, or  pure  gold  may  be  bought  for  the  purpose 

In  the  assay  proper,  if  gold  is  required  it  is  weighed, 
added  at  once  to  the  weighed  assay,  and  the  whole  cu- 
pelled with  a  suitable  quantity  of  sheet-lead.  The  dif- 
ference between  the  weight  of  the  bead,  and  that  of  the 
assay  'plus  the  added  gold,  represents  base  metal.  The 
bead  being  laminated,  parted,  etc.,  the  further  loss  of 
weight  is  the  silver  fineness  to  which  a  correction  may 
be  added,  according  to  the  judgment  and  experience  of 

*A  larger  surcharge  is  allowed  for  very  small  bars  than  for  large  ones; 
also  when  a  little  base  metal  is  believed  to  be  present,  the  bar  being 
brittle,  etc. 


AND    SILVER   BULLION.  43 

the  workman,  for  cupellation  loss,  from  one  to  three  or 
more  points.  Finally,  the  weight  of  the  cornet,  less  that 
of  the  added  gfold  and  a  suitable  allowance  for  surcharge 
is  the  gold  fineness.  Except  in  particular  cases,  the  in- 
quartation  by  addition  of  gold  is  generally  neglected. 

If  an  addition  of  silver  is  necessary,  as  for  instance 
in  the  case  of  a  bar  which  is  about  half  gold,  it,  like 
the  gold,  may  be  added  at  once,  and  allowed  for  in  the 
final  estimation  of  the  silver  fineness.  It  is  perhaps  bet- 
ter to  cupel  the  assaj'"  with  the  requisite  quantity  of  lead 
to  clear  it  of  base  metal;  note  the  weight  of  the  bead, 
then  add  the  silver  and  cupel  with  a  very  light  lead 
cornet,  laminate,  part,  etc..  and  weigh  the  gold.  The 
difierence  between  the  gold  fineness  and  the  weight  of 
the  bead  after  the  fir^t  cupellation,  plus  a  suitable  cor- 
rection for  loss,  is  the  silver  fineness.  By  operating  in 
this  way  the  cupellation  loss  of  the  added  silver  need 
not  be  considered. 

Example:  A  thousand  of  doree  bullion  containing 
some  copper,  was  cupelled  with  12,000  of  lead,  and  gave 
a  bead  weighing  900.  It  being  supposed  to  contain  too 
much  gold  for  parting,  2,000  of  silver  were  added,  and 
the  whole  wrapped  in  lead  and  again  cupelled,  then 
parted.  The  gold  weighed  400.  Deducting  400  from 
900  left  500  for  the  approximate  weight  of  the  silver. 
In  the  assay  proper  400x2.5  =  1,000  of  silver  was  requi- 
site ;  the  bullion  contained  500,  hence  500  of  silver  must 
be  added. 

One  thousand  of  the  bullion  was  then  cupelled  with 
8,000  of  lead,  and  gave  a  bead  weighing  907.  This  was 
again  cupelled  with  500  of  silver  and  a  small  lead  cornet, 


44  ASSAYING   GOLD 

then  laminated,  parted,  etc.  The  gold  was  in  a  single 
piece  and  weighed  401.  The  bar  was  therefore  401  fine 
gold,  and  907  —  401=506  fine  silver,  to  which  a  point 
might  be  added  for  cupellation  loss.  Unless,  in  partic- 
ular cases,  or  for  quite  large  bars,  the  process  indicated 
for  the  preliminary,  if  executed  with  skill  and  judg- 
ment, answers  all  purposes. 

Base  Bar. — This  assay  is  better  scorified  before  cu- 
pellation. An  approximation  to  the  quantity  of  lead 
required,  and  to  the  gold  and  silver  fineness,  may  first 
be  obtained  by  cupelling  1,000  of  the  bullion  with  as 
much  lead  as  may  be  found  necessary  for  clearing  the 
bead.  Beginning  with  the  quantity  of  lead  which  is 
judged  to  be  required,  and  watching  the  operation,  more 
lead  can  be  added  from  time  to  time  until  the  bead  is 
seen  to  round  up,  and  to  exhibit  the  brilliant  play  of 
colors  immediately  preceding  the  brightening.  Silver 
is  to  be  added,  if  supposed  to  be  requisite  for  the  part- 
ing; it  must  be  weighed.  In  the  assay  proper,  1,000  of 
the  bullion  may  be  scorified  with  the  proportion  of  lead 
found  necessary  in  the  preliminary,  and  a  little  borax. 
When  the  scorification  has  been  carried  far  enough,  the 
assay  may  be  poured,  or  cooled  in  the  scorifier  and  that 
broken,  the  button  placed  on  a  hot  cupel,  and  any  de- 
sired addition  of  gold  or  silver  made.  The  gold  or  silver 
must  be  weighed,  wrapped  in  sheet-lead,  and  added  to 
the  button  after  that  is  melted ;  or,  the  addition  of  silver 
may  be  deferred  until  the  bead  is  cleared,  cleaned,  and 
weighed,  as  in  the  assay  of  a  dore  bar,  and  for  the  same 
reason,  yet  if  the  bullion  contains  much  copper,  and  but 
little  silver  in  proportion  to  the  gold,  it  is  better  not  to 


AND   SILVER   BULLION.  46 

postpone  the  addition  of  silver,  because,  in  the  cupel lation 
of  gold  and  copper,  without  a  considerable  proportion 
of  silver,  some  gold  is  lost.  For  this  reason  on  the  other 
hand,  the  addition  of  gold  when  much  copper  is  present 
is  better  postponed  until  the  copper. has  been  removed. 
Neither  gold  nor  silver  should  be  added  during  the  scori- 
fication  as  needless  losses  are  incurred  thereby,  all  of 
which  will  inure  to  the  detriment  of  the  bullion.  It 
has  been  observed  by  experimenters,  that  if  gold  is  added 
to  lead  already  melted  on  a  cupel,  little  or  no  loss  occurs, 
but  if  the  gold  be  previously  scorified  with  lead,  and 
then  cupelled,  there  is  a  notable  loss.  As  with  dore 
bullion,  the  inquartation  by  addition  of  gold  is  not  gen- 
erally practiced.  Where  so  much  lead  is  used  as  some- 
times in  the  assay  of  base  bullion,  it  need  not  be  all  sheet- 
lead;  pieces  of  assay  bar-lead  may  be  used  on  the  cupel, 
and  either  that  or  granulated  lead  in  the  scorifier,  so  that 
sheet  is  only  required  for  wrapping  the  assay  and  the 
gold  or  silver  for  the  inquartation,  for  which  it  is  safer 
than  the  paper  r-ecommended  by  some  writers,  though 
paper  may  be  used  in  case  of  need. 

Example  of   assay  of    base  bar   containing  lead  and 
copper : — 
Preliminary  cupellation  without  addition, 

gave  a  coppery  bead,  weighing 732 

Showing  that  the  assay  contained  about 2<)8  lead 


Recupelled  with  10  parts  =  7320  lead 

Did  not  clear;  added  2  parts  =  1404  lead 

Which  cleared  the  bead.     Total  lead 8784 


46  ASSAYING    GOLD 

The  bead  weighed 327 

Added  an  equal  weight  of  silver;  cupelled  and 

parted,  gold  weighed 4.7 

Silver ; .      280 

In  the  assay  proper,  1000  scorified  with   8500  of  lead 
and  cupelled  with  addition  of  %^^  —  ^"J  =z 
65  gold,  weighed 396 

Parted;  gold  weighed 112^ 

Silver  weighed 283^ 

True  weight  of  gold  (after  deduction  of  65  added 

from  the  total) 47i 

The  assay  therefore  shows  the  bar  to  contain  in  1 

part,  fine  gold 0.0475 

"     silver  . 0.2835 

Base  metal 0.6690 


1.0000 
If  the  proportion  of  gold  to  silver  had  been  reversed, 

the  bead  from  the  pieliminary  would  have  been  yellotvr. 

We  should  then  have  added  twice  its  weight  of  sil  ^  er  in 

the  preliminary  (see  Part  I,  page  76),  and  2.5  times  280 

of  silver  in  the  assay  proper. 

The  following  table,  from   Mitchell,  will  give  an  idea 

of  the  proportion  of    lead   required  to  separate    copper 

from  gold  by  cupellation:^- 


AND   SILVER   BULLION.  47 

GOLD  IN  ALLOY.  LEAD  REQUIRED. 

.900..  .f 10  parts 

.800 ...    16     " 

.700 22     " 

.600 24     " 

.500  ) 

to    [  34     " 

.050  ) 
For  alloys  of  copper  and  silver,  about  half  the  above 
proportions  of  lead  suffice,  but  in  both  cases  much  de- 
pends on  the  temperature  of  the  muffle  and  on  other  con- 
ditions. The  guide  is  the  condition  of  the  button ;  if  it 
is  hard,  brittle,  or  coppery,  it  must  be  treated  with  a 
fresh  quantity  of  lead. 

Gold  and  Platinum. — The  presence  of  platinum  in 
the  assay  is  known  by  the  following  signs:  The  brighten- 
ing of  the  bead  requires  a  much  higher  heat  than  usual, 
and  is  less  vivid.  The  bead  is  flat,  thick  edged,  and  dull. 
On  parting,  if  the  platinum  is  in  the  proportion  of  1  to 
50  of  gold,  the  acid  is  colored  straw  yellow.  The  an- 
nealed cornet  is  paler  than  usual,  even  to  resembling 
tarnished  silver.  It  is  important  to  recognize  the  pres- 
ence of  platinum  in  gold  bullion,  lest  it  be  mistaken  for 
silver,  because,  while  not  removed  by  cupellation,  it  is 
dissolved  in  the  parting.  In  order  that  the  parting  may 
be  efl*ected  in  the  presence  of  platinum,  the  quantity  of 
silver  alloyed  must  be  as  much  as  twice  the  weight  of 
the  gold  and  platinum  together,  and  as  both  the  silver 
and  the  platinum  are  dissolved  in  the  ordinary  partmg 
with  nitric  acid,  it  may  happen  that  the  gold  will  crum- 
ble. 


48  ASSAYING   GOLD 

An  alloy  of  gold  and  platinum  with  12  parts  of  silver 
may  be  parted  by  boiling  in  sulphuric  acid,  leaving  the 
gold  and  platinum,  the  silver  alone  being  dissolved.  The 
gold  and  platinum  are  washed  with  hot  water,  dried  and 
weighed;  then  again  alloyed  with  2J  parts  of  silver  and 
parted  with  nitric  acid,  leaving  the  gold,  which  is  washed, 
dried,  and  weighed.  The  more  usual  method  is  to  make 
an  alloy  with  enough  silver  to  part  in  nitric  acid,  which 
leaves  the  gold ;  then  to  precipitate  the  silver  from  the 
liquid,  in  the  form  of  chloride,  by  adding  hydrochloric 
acid.  The  silver  chloride  is  separated  from  the  liquid 
by  filtration  or  by  decantation  (pouring  off),  dried 
and  weighed;  75  per  cent,  of  the  weight  is  silver,  from 
which  the  weight  of  the  added  silver  must  be  deducted, 
leaving  the  silver  fineness  of  the  bullion.  To  the  liquid 
containing  the  platinum  is  added  a  little  hydrochloric 
acid,  and  then  solution  of  ammonium  chloride  as  long  as 
a  precipitate  forms.  The  liquid  is  then  evaporated  to 
dryness,  and  to  the  residue,  when  cold,  dilute  alcohol  is 
added,  and  the  insoluble  portion  (platinum  ammonium 
chloride)  collected  on  a  filter,  washed  with  alcohol,  dried 
and  heated  to  redness.  The  residue  is  platinum,  which  is 
weighed.  The  united  weight  of  the  gold  and  platinum, 
deducted  from  that  of  the  cupelled  bead  (minus  any 
added  silver),  leaves  the  silver  fineness  of  the  bullion, 
which  should  agree  nearly  with  that  found  by  calcula- 
tion from  the  precipitated  chloride  as  above. 

Iridium  does  not  form  an  alloy  with  the  gold.  It 
mostly  falls  out  of  the  cornet  during  the  lamination,  in 
the  form  of  scales  of  a  steely  color.  If  in  large  quan- 
tity, a  part  may  be  found  at  the  bottom  of  the  pot  in 
which  the  bullion  is  melted. 


AND   SILVER   BULLION.  49 

Silver  Bar. — Silver  bullion  usually  contains  copper  or 
lead,  or  both.  The  proportion  of  lead  required  to  remove 
the  copper  depends  on  that  of  the  copper  to  the  silver. 
If  the  quality  of  the  bullion  is  not  approximately 
known,  it  may  be  ascertainea  by  a  preliminary  cupel la- 
tion  with  as  much  lead  as  may  be  found  necessary.  The 
assay  proper  is  then  treated  accordingly.  Any  lead 
which  the  bullion  may  contain  is  counted  as  a  part  of 
that  required,  hence  if  the  bullion  contains  some  lead, 
1,000  of  it  may  be  cupelled  without  other  addition  than 
the  small  piece  of  sheet-lead  necessary  to  envelop  it.  If 
the  bead  clears,  no  further  addition  is  required;  if  not, 
lead  is  added  in  successive  small  portions  until  it  does, 
and  the  quantity  of  lead  so  added  is  approximately  that 
which  will  be  requisite  in  the  assay  proper.  A  table 
will  be  given  which  will  aid  in  the  apportionment. 

If  much  lead  is  required,  it  is  best  to  melt  the  greater 
portion  of  it  on  the  cupel  before  adding  the  assay ;  bar- 
lead  should  be  employed  in  this  case.  When  the  lead  is 
quite  melted,  the  assay  is  added,  enveloped  as  usual  in  a 
lead  capsule,  the  weight  of  which  makes  up  the  required 
quantity.  In  order  to  make  a  proper  correction  for  the 
cupellation  loss,  a  test  assay  is  made  at  the  same  time 
and  in  the  same  heat.  Test  silver  and  copper  are  weighed 
off  in  the  proportions  in  which  they  exist  in  the  bullion, 
as  nearly  as  may  be  judged,  or  as  indicated  by  the  pre- 
liminary if  made,  and  cupelled  with  the  same  weight  of 
lead  as  is  used  for  the  assay.  The  loss  sustained  by  the 
test,  or  for  safety,  a  point  less,  is  added  to  the  result  of 
the  assay.  Unless  the  bar  is  quite  small,  two  assays, 
one  from  each  of  the  two  samples,  should  be  made, 
and  should  agree  within  a  point. 


50  ASSAYING   GOLD 

The  cupellation  must  be  conducted  with  great  care  as 
to  heat.  I  have  known  as  much  as  30  points  to  be  lost 
by  unskillful  cupellation,  and,  although  a  test  or  check 
assa}'  may  be  made  with  each  bullion  assay,  or  in  the 
mifist  of  a  group  of  those,  oi  approximately  similar  qual- 
ity, yet,  when  losses  are  excessive  the  check  cannot  be 
implicitly  relied  on  for  the  correction.  Tables  of  the  loss 
for  bullion  of  various  grades  of  fineness  are  oriven  in 
books,  but  are  only  useful  as  showing  what  has  been, 
and  therefore  can  be,  done.  The  loss  should  seldom  be 
so  much  as  10  points,  and  with  bullion  that  is  nearly 
fine  should  not  exceed  3. 

The  smoke  from  the  cupels  should  rise  to  about  the 
middle  of  the  mufiie,  the  draught  through  that  not  being 
so  strong  as  to  draw  it  immediately  through  the  holes,  a 
part  generally  escaping  by  the  front.  If  much  lead  is 
used,  crystals  of  litharge  should  form  on  the  cupel  at  a 
little  distance  from  the  bead,  and  even  the  brightening 
heat  should  not  cause  them  to  disappear.  This  is  called 
"  feathering"  the  cupel.  When  the  bullion  is  so  fine  as 
to  require  but  little  lead,  it  is  scarcely  possible  to  feather 
the  cupel  without  great  risk  of  freezing  the  assay,  and 
an  assay  once  frozen,  even  though  remelted,  is  not  reli- 
able. 

On  account  of  the  delicacy  of  this  operation  and  the 
occasional  necessity  for  moving  a  cupel  during  its  prog- 
ress, as  well  as  at  the  finishing,  only  a  small  number  of 
assays  can  be  properly  made  at  once  in  a  muffle  which  is 
only  4  or  5  inches  wide.  When  the  bead  is  about  to 
brighten,  it  should  be  pushed  further  back  where  the  heat 
is  higher,  or  a  glowing  coal  may  be  placed  before  it;  it 


AND   SILVER   BULLION.  51 

must  remain  in  this  higher  heat  only  a  few  seconds  after 
the  brightening,  say  while  5  can  be  deliberately  counted ; 
it  must  then  be  cooled  with  the  precautions  indicated  in 
Part  I,  page  67,  the  best  portion  of  which,  being  a 
method  not  generally  published,  may  be  repeated  here. 

The  cupel  is  drawn  to  the  front  of  the  muffle,  and 
gently  tapped  on  one  side  by  the  tongs.  At  the  instant 
when  the  bead  ceases  responding  to  the  taps  by  its  vibra- 
tion, and  a  certain  change,  which  will  be  recognized 
when  once  seen,  comes  over  it  and  the  face  of  the  cupel, 
indications  of  the  solidification  of  the  bead,  it  is  pushed 
back  into  the  hottest  part  of  the  muffle,  and  there  left 
for  a  minute  or  thereabout,  after  which  it  will  not 
sprout,  being  solidified  all  through,  as  shown  by  a  dimple 
on  its  surface  caused  by  contraction.  The  heat  must  not 
be  so  intense  as  to  remelt  the  bead,  or  the  effect  desired 
will  be  lost,  as  will  also  some  silver;  but  a  bead  is  not 
very  easily  remelted  when  once  chilled.  The  bead  must 
be  white,  well  rounded,  slightly  adherent  to  the  cupel, 
and  crystalline  at  the  bottom  when  cleaned.  It  is 
weighiid,  and  then  parted  without  addition  of  gold  to 
inquartate.  Any  gold  found  is  cupped,  dried,  weighed, 
giving  the  gold  fineness,  which,  deducted  from  the  weight 
of  the  bead,  leaves  the  silver  fineness  to  which  is  added 
a  correction  indicated  by  the  check.  The  following 
table  from  Mitchell  gives  the  approximate  proportion  of 
lead  required  for  the  cupellation  of  different  alloys  of 
silver  with  copper: — 


52  ASSAYING   GOLD 

SILVER  IN  ALLOY.  LEAD  REQUIRED. 

1.000  (pure  silver) 300 

.950 3.000 

.900 7.000 

.800 10.000 

.700 12.000 

.600 14.000 

.500  to  pure  copper 17.000 

The  reason  that  1,000  of  pure  silver  requires  300  of 
lead  is  that  silver  alone  cannot  be  melted  on  the  cupel 
without  its  throwing  off  minute  globules,  nor  can  a  good 
bead  be  formed  without  the  aid  of  lead;  so  that  no  mat- 
ter how  nearly  pure  the  silver  may  be,  that  quantity  of 
lead,  at  least,  must  be  used. 

Silver  Lead. — This  assay  is  very  simple.  It  is  only 
necessary  to  wrap  the  weighed  assay  in  a  lead  capsule,  in 
order  to  ensure  the  union  of  all  fragments,  and  cupel  it 
with  the  usual  precautions.  A  better  way  is  to  take 
several  thousands  of  the  sample,  and  scorify  with  a  little 
powdered  glass  or  quartz,  repeating,  if  needful,  until  the 
button  is  of  a  suitable  weight,  and  then  cupel.  The 
bead  should  be  parted,  and  results  must  be  divided  ac- 
cording to  the  number  of  thousands  used  for  the  assay. 
The  value  of  silver  lead,  in  precious  metal,  is  usually 
reported  as  so  many  ounces  of  gold  and  so  many  of 
silver  in  the  ton,  hence  an  assay  ton  (Part  I,  page  80), 
or  any  quantity  commonly  used  for  ore  assays  may  be 
taken,  being  weighed  on  the  pulp  scales,  scorified  and 
cupelled,  and  value  calculated  as  for  ore.  Or,  the  fine- 
ness in  points  divided  by  10  is  the  percentage  from 
which  ounces  or  values  per  ton  can  be  reckoned.  (See 
Part  I,  76.) 


AND   SILVER   BULLION.  53 

To  Find  the  Value  of  a  Bar. — The  weight  of  the  bar 
in  troy  ounces  multiplied  by  the  gold  fineness  (stated  in 
thousandths),  gives  the  weight  of  pure  gold  contained,  the 
value  of  which  is  computed  at  $20.67  per  ounce.  The 
weight  of  the  bar,  multiplied  by  the  silver  fineness  (stated 
in  thousandths),  gives  the  weight  of  pure  silver  contained. 
Silver  is  reckoned  at  $1.2929+  per  ounce. 

The  abov^e  values  of  pure  gold  and  silver,  multiplied  by 
the  fineness  of  the  bar  in  each  metal  (stated  in  thou- 
sandths), gives  the  value  per  ounce  of  such  bullion  for  each 
metal ;  and  the  weight  of  the  bar,  multiplied  by  the  re- 
spective values  per  ounce,  gives  the  value  of  the  entire 
bar  for  each.  It  is  well  to  make  the  calculation  in  both 
ways,  in  order  that  the  one  may  check  the  other. 

The  dealers  in  assayers'  goods  distribute,  gratuitously, 
sets  of  tables  showing  tlie  value  per  ounce  of  bullion  of 
any  fineness  in  gold  or  silver.  The  value  per  ounce  be- 
ing found  from  these  tables,  it  only  remains  to  multiply 
the  weight  of  the  bar  in  troy  ounces  by  that. 

The  value  per  ounce  of  bullion  of  any  fineness  may 
be  found  by  means  of  the  "  Assay  Table  for  One  Assay 
Ton  of  Ore  "  on  page  106  of  Part  I,  with  more  accuracy 
than  by  calculation,  unless  a  great  number  of  figures  be 
used.  One  ounce  of  bullion  1,000  fine  is  of  the  same 
value  as  1,000  ounces  1  fine,  or  372  ounces  1,000  fine 
equals  1,000  ounces  372  fine,  and  so  of  any  fineness. 
Hence,  to  find  the  value  of  1  ounce  of  bullion  of  any 
given  fineness,  consider  the  points  of  fineness  as  so  many 
ounces  1,000  fine,  and  find  the  value  of  that  quantity  as 
directed  for  an  ore  assay.  Divide  by  1,000  (move  the 
decimal   point);  the   result   is   the   value   of  one   ounce. 


64  ASSAYING    GOLD 

Example:  What  is  the  value  per  ounce  of  silver  bullion 
.840  fine  ? 

800  ounces  1,000  fine= $1034.84 
40      "  "       "   =        51.72 

$1086.06 
This  divided  by  1000  gives  $1,086,  the  value  of  1  ounce. 
A  similar  process  gives  the  value  for  gold. 

To  find  the  value  of  any  number  of  ounces  of  bullion 
of  any  fineness  by  the  same  table,  multiply  the  weight 
by  the  fineness;  the  result  is  the  weight  of  pure 
metal,  gold  or  silver  as  may  be.  Find  the  value  of  the 
pure  metal  as  directed  for  ore  assays. 

Example:  A  silver  bar  weighs  1,642  ounces  and  is  .840 
fine.      What  is  its  value  ? 

l,642x. 840  =  1,379.28   ounces  of   pure  silver;  then  from 
the  table: — 

1,000  ounces $1292.93 

300 


70 

9 

0.2 
0.08 


387.88 

90.50 

11.63 

0.26 

1 

1379.28  $1783.21 

This  use  of  the  table  is  much  facilitated  when  it  is  ar- 
ranged so  that  two  figures  can  be  operated  on  at  once,  in 
which  form  I  have  all  these  tables ;  but  they,  especially 
the  gold  tables,  contain  too  many  figures  for  this  book, 
being  calculated  to  9  and  10  places  from  a  valuation  of 
$20.671834625323  per  ounce  of  gold. 


AND   SILVER   BULLION.  56 

It  often  happens,  in  the  country,  that  a  bar  must  be 
weighed  in  avoirdupois  pounds.  One  pound  avoirdupois 
is  equal  to  7,000  grains  troy,  or,  14.583-}-  ounces.  Multi- 
plying the  pounds  and  decimal  fractions  by  the  latter 
number  converts  them  into  troy  ounces.  The  number  of 
troy  ounces  corresponding  to  any  number  of  avoirdupois 
pounds  may  be  found  very  simply  and  accurately  from 
the  assay  table  for  20  grammes  of  ore,  on  page  104  of 
Part  I,  by  proceeding  as  there  directed ;  or,  the  value  of 
a  bar,  of  which  the  weight  is  given  in  pounds,  m*ay  be 
got  without  finding  the  ounces.  Again,  the  value  of 
pounds  and  ounces  avoirdupois  may  be  computed  by  the 
aid  of  the  following  table,  after  multiplying  the  weight 
of  the  bar  by  the  fineness,  in  gold  and  silver  respectively, 
for  the  contained  weight  of  the  pure  metals. 

GOLD.  SILVER. 

1  pound $301.46 $18.85 

1  ounce 18.84 1.17 

i      "      4.76 0.29 

i      "      2.38 0.14i 


1 


1.19 0.07i 


56  ASSAYING   GOLD 


HUMID  ASSAY  OF    SILVER  BULLION. 


Owing  to  the  uncertainty  attending  the  fire  assay  of 
silver  bullion,  the  humid  method  is  used  in  all  United 
Stated  mints  and  first-class  private  offices.  This  method 
depends  on  the  fact  that  silver  in  nitric  acid  solution  is 
completely  precipitated  in  the  form  of  chloride  by  a  solu- 
tion of  common  salt.  At  the  same  time  the  salt  is  de- 
composed, so  that,  if  suitable  proportions  of  silver  and 
salt  be  thus  brought^  together,  neither  can  afterward  be 
found  in  the  liquid. 

In  the  Royal  Mint  of  India,  the  precipitated  silver 
chloride  is  dried  and  weighed,  and  from  its  weight  that 
of  the  pure  silver  is  calculated.  In  this  country  and  in 
Europe,  the  quantity  of  silver  in  the  solution  is  estimated 
by  the  quantity  of  salt  solution  of  known  strength 
requisite  for  its  precipitation.  The  salt  solution  is  either 
weighed  or  measured.  The  latter  method  is  the  most  gen- 
eral, and  is  called  the  volumetric  assay. 

A  solution  of  salt  in  water  is  made,  of  which  100  cubic 
centimeters  will  exactly  precipitate  1,000  ff  pure  silver, 
leaving  neither  salt  nor  silver  in  the  liquid.  This  is  the 
noronal  solution.  The  thousand  used  in  this  assay  is 
either  10  grains  or  1  gramme,  the  latter  generally.  An- 
other solution  of  salt  is  made  one-tenth  as  strong  as  the 
normal;  consequently  1  cubic  centimeter  of  it  precipitates 


AND  SILVER  BULLION. 


57 


one  point  of  silver.  This  is  the  decime  salt  solution.  A 
decime  solution  of  silver  is  also  prepared,  of  which  1  cu- 
bic centimeter  contains  one  point  of  silver;  consequently 
the  two  decime  solutions  are  equivalent,  volume  for  vol- 
ume, each  neutralizing  the  other.  The  sign  for  a  cubic 
centimeter  is  c.  c. 

Measuring  the  Normal  Solution. — A 
glass  pipette  containing  100  c.  c.  is  used. 
The  accompanying  diagram  and  directions 
are   from  Mitchell.     "Immerse  the  jet   (c) 
of    the  pipette   in  the  solution,  apply   the 
mouth  to   the   upper  orifice,  and  draw  the 
liquid  into  d,  above  the  circular  mark,  ab. 
Dexterously  apply  the  forefinger  of  one  of 
the  hands  to  this  orifice,  remove   the  pipette 
from  the  liquid,  and  hold  it  as  represented  in 
the  figure.     The  mark  ah  is  held  on  a  level 
witli  the  eye,  and  the  surface  of  the  solution 
allowed  to  descend  until  it  forms  a  tangent 
with  the  plain  ah.     At  this  instant   the  jet 
-    c  of  the  *pipette  is  set  at  liberty  by  remov- 
_  ing  the  finger  against  which  it   had  been 
Y y^   pressed,  and,  without    otherwise  changing 
Ql     I,    the  position  of  the  hands,  the  contents  are 
J^^^^  allowed  to  run  into  the  bottle  appropriated 
Cy  for  that   purpose  "  (containing  the   assay), 

"  taking  care  to  remove  the  pipette  as  soon  as  the  stream 
stops." 

"  If,  after  having  filled  the  pipette  by  aspiration,  there 
is  any  difficulty  found  in  a  sufficiently  rapid  application 
of  the  forefinger  to  the  superior  orifice  to  prevent  the  fall 


\ 


58  ASSAYING  GOLD 

of  the  liquid  below  the  mark  ah,  the  pipette  must  be  re- 
moved from  the  liquid,  the  orifice  being  closed  by  pressing 
the  tongue  against  it ;  then  apply  the  middle  finger  of  one 
of  the  hands  to  the  lower  orifice,  remove  the  tongue,  and 
apply  the  forefinger  of  the  other  hand  to  the  larger  orifice, 
previously  wiped  dry,"  The  pipette  should  be  rinsed 
with  a  little  of  the  solution  before  being  charged,  and 
washed  twice  with  water  after  use. 

Measuring  the  Decime  Solutions. — The  decime  so- 
lutions are  measured  in  smaller  pipettes  gauged  so  that, 
when  filled  to  the  mark  c  d,  they  allow  1  c.  c.  to  run  freely, 
the  small  quantity  of  the  solution  remaining  in  the  pipette 
not  forming  part  of  the  c.  c.  The  decime  salt  solution  is 
kept  in  a  bottle,  closed  by  a  cork  which  is  traversed  by 
the  pipette  firmly  fixed  in  a  hole  bored  for  that  purpose. 
The  decime  silver  solution  is  kept  in  a  bottle  closed  by  a 
glass  stopper.     Quoting  Mitchell  again: — 

•'  To  measure  a  thousandth  ('  point ')  with  the  pipette, 
the  bottle  is  held  with  one  hand,  and  the  pipette  with  the 

S  other.     The  pipette  is  taken  from  the 

solution  after  its  upper  orifice  has  been 
closed  by  the  forefinger;  the  lower  or- 
ifice is  then  inclined  against  the  edge 
of  the  flask  to  remove  the  liquid,  which, 
without  this  precaution,  would  remain 
there ;  the  mark  c  d  is  then  raised  to 
the  level  of  the  eye,  and,  by  a  suitable 
pressure  of  the  forefinger  on  the  upper 
orifice,  which  may  be  obtained  by 
giving  the  pipette  a  slight  alternat- 
ing circular  movement  between  the 
fingers,  the  solution   is  allowed   to  run  out  gradually. 


AND   SILVER  BULLION.  59 

The  instant  the  concave  surface  of  the  liquid  is  at  the 
level  c  d,  the  pipette  is  firmly  closed  by  pressure  of  the 
forefinger  on  its  orifice,  which  is  held  above  the  bottle 
into  which  the  solution  is  to  be  poured,  and  the  forefinger 
removed  so  that  it  can  be  emptied.  It  is  here  necessary 
to  remark  that  in  order  to  regulate  the  slow  and  regular 
runnings  of  the  liquid  from  the  pipette,  by  the  pressure 
of  the  forefinger,  the  latter  ought  to  be  neither  too  moist 
nor  too  dry;  if  too  dry,  it  will  not  perfectly  close  the 
orifice,  even  by  strong  pressure;  if  too  moist  it  pre 
vents  the  entrance  of  air,  and  the  liquid  will  not  run 
or  if  it  does  it  will  be  irregularly."  (This  observation 
should  not  be  lost  sight  of  in  the  use  of  the  large 
pipette.)  As  it  is  often  convenient  to  use  several  c.  c.  of 
either  decime  solution  at  once,  the  pipettes  are  grad- 
uated from  1  to  5. 

Preparation  of  the  Normal  Solution. — One  thou- 
sand of  silver  requires  541.664-  of  salt,  hence  1  gramme 
of  silver  requires  0.5417  gramme,  or  10  grains  require 
5,417  grains.  It  is  more  troublesome  to  prepare  pure  salt 
and  to  measure  pure  water  witli  perfect  accuracy,  than 
to  make  a  solution  which  approaches  the  required  stand- 
ard, and  then  rectify  it  by  an  addition  of  salt  or  water^ 
as  indicated  by  the  result  of  an  assay  of  pure  silver,  or 
silver  of  known  fineness,  made  with  it. 

The  easiest  way  in  which  to  prepare  the  approxima- 
tive solution  is  to  make  a  saturated  solution  of  good 
table  salt,  and  to  dilute  a  certain  quantity  of  that  to  the 
required  strength.  Take  about  a  pound  of  salt  and  dis- 
solve it  in  about  four  times  its  weight  of  water.  Filter 
the  solution,  and  boil  it  down  to  a  quarter  of  the  original 


60  ASSAYING   GOLD 

quantity,  or  less,  causing  the  deposition  of  the  greater 
part  of  the  salt.  Pour  off  the  liquid,  and  wash  the  salt 
quickly  with  water.  Redissolve  the,  salt  in  as  little  wa- 
ter as  will  suffice,  and  again  evaporate  until  a  little  of  it 
is  again  deposited.  Cool  the  liquid  and  put  it  into  a 
bottle.  The  liquid  is  a  saturated  solution  containing  26.5 
per  cent,  of  its  weight  of  salt,  as  nearly  as  can  be  ascer- 
tained. One  hundred  c.  c.  of  this  sol  ution,  at  60°  F.  contains 
enough  salt  for  49  assays  if  the  thousand  be  1  gramme, 
or  for  75.5  assays  if  the  thousand  be  10  grains.  There- 
fore, for  the  gramme  system  take  1  litre  (or  10  charges 
of  the  large  pipette)  of  this  solution,  and  add  48  litres  of 
water  to  make  normal  solution  for  490  assays;  or,  take 
2.08  volumes  of  the  saturated  solution,  and  97.92  volumes 
of  water.  For  the  grain  system  take  1  litre  of  satur- 
ated solution  to  74. 5  litres  of  water  to  make  normal  solu- 
tion for  755  assays;  or  take  1 1  volume  of  saturated  solution 
and  98.66  volumes  of  water.  If  more  convenient,  take 
for  the  gramme  system  5  parts  by  any  kind  of  weight, 
of  saturated  solution,  and  189  parts  by  weight  of  water, 
or  1  to  37.88.  For  the  grain  'system,  1  part,  by  any 
kind  of  weight,  of  the  saturated  solution  to  58.89  of 
water. 

If  preferred,  pure  salt  may  be  made  by  neutralizing 
pure  hydrochloric  acid  with  pure  sodium  carbonate  or 
bicarbonate,  evaporating  to  dryness  and  heating  almost 
to  redness.  The  mass  should  be  powdered  a  nd  kept  in  a 
stoppered  bottle.  Nearly  pure  salt  may  be  prepared  by 
dissolving  table  salt  in  water,  boiling  until  a  large  pro- 
ppqrtion  of  the  salt  is  deposited,  pouring  off  the  liquid, 
washing  the  salt  thrice  with  a  little  water,  ai^d  drying, 


AND   SILVER   BULLION.  61 

first  between  sheets  of  blotting  paper,  and  then  by  heat- 
ing almost  to  redness.  In  making  normal  solution  from 
the  dry  salt,  take  for  each  litre  of  water  5.417  thousands 
of  salt,  which  is  5.417  grammes  or  54.17  grains  accord- 
ing to  the  weights  used  for  the  assays.  The  most  suit- 
able way  in  which  to  operate  is  to  place  the  salt,  weighed 
for  the  required  number  of  litres  of  solution,  into  the 
litre  flask,  and  add  a  sufficient  quantity  of  water  to  dis- 
solve it  easily;  when  the  salt  is  completely  dissolved,  fill 
the  flask  to  the  mark  with  water,  and  empty  it  into  a 
carboy;  again  fill  the  flask,  and  pour  the  water  into  the 
carboy,  as  many  times  as  may  be  necessary  to  make  the 
desired  quantity  of  solution.  Or  take  10  pounds  avoir- 
dupois weight  of  water  and 

for  1  gramme=  1,000 — 24.61  grammes 
*•    10  grains  =1,000—246.0  grains 
Of  salt.     Dissolve  the  salt  in  a  small  portion  of  the  water 
and  add  the  remainder. 

The  solution,  in  whatever  way  prepared,  must  be 
thoroughly  mixed.  This  may  be  done  by  rolling  and 
shaking  the  containing  vessel,  or  by  stirring  with  a  wand. 
The  plan  recommended  when  dry  salt  is  used,  of  dissolv- 
ing it  first  in  a  small  portion  of  the  water,  makes  it  easier  to 
be  sure  that  it  is  all  dissolved  than  if  it  were  added  to 
the  whole  quantity  of  the  water  in  the  larger  vessel. 
The  mixing  of  the  solution  with  the  rest  of  the  water  is 
not  difficult. 

Preparation  of  the  Decime  Salt  Solution. — Any 
volume  of  the  normal,  diluted  with  9  such  volumes  of 
water  makes  a  decime  solution.  Measure  with  the  large 
pipette  100  c.  c.  of  water,  which  pour  into  the  appropri- 


62  ASSAYING    GOLD 

ate  bottle;  remove  10  c.  c.  of  the  water,  by  means  of  one 
of  the  small  pipettes,  and  replace  it  by  an  equal  volume 
of  normal  solution ;  mix  by  shaking ;  this  small  quantity 
is  for  use  in  correcting  the  standard  of  the  normal ;  after 
this  has  been  done,  a  new  decime  solution  must  be  pre- 
pared if  the  error  of  the  normal  was  considerable,  and  a 
larger  quantity  will  be  required.  To  prepare  it  measure 
1  litre*  of  water,  or  weigh  1,000  grammes  at  60^ 
Fahrenheit;  remove  100  c.  c.  of  the  water,  and  replace 
it  by  100  c.  c.  of  the  corrected  normal  solution,  by  means 
of  the  large  pipette. 

Preparation  of  the  Decime  Silver  Solution. — One 
thousand  of  pure  silver  is  dissolved  in  about  7  c  c.  of 
nitric  acid  in  a  litre  flask,  and  the  flask  is  then  filled  to 
the  mark  with  distilled  water;  or  at  least  with  water 
which  does  not  cause  the  slightest  turbidity.  If  a  litre 
flask  is  not  at  hand,  1,000  grammes  of  water  (15,432 
grains)  at  60°  Fahrenheit  may  be  weighed,  a  volume  of 
it  equal  to  that  of  the  silver  solution  removed  by  means 
of  a  pipette,  and  the  remainder  added  to  the  silver  solu- 
tion. This  quantity  will  suffice  for  a  very  considerable 
number  of  assays,  and  as  it  will  inevitably  become 
stronger  by  evaporation  if  long  kept,  it  may  be  as  well 
to  make  a  smaller  quantity;  it  is  only  necessary  that 
each  c.  c.  of  it  shall  contain  a  point  of  silver  and  not 
more. 

Standardizing  the  Normal  Solution. — A  thousand 
of  pure  silver  is  dissolved  in  about  10  grammes  of  nitric 
acid  of   about  32°   Baumt^,  in  a  bottle   of   clear    glass 

*A  litre  is  1,000  c.  c. 


AND  SILVER  BULLION. 


63 


which  will  contain  about  200  c.  c.  To  facilitate  the 
action,  the  bottle  is  placed  in  a  vessel  containing  warm 
water.  When  the  silver  is  dissolved,  the  red  fume  which 
fills  the  bottle  is  blown  out  by  means  of  an  inserted  glass 
tube  so  bent  as  that  the  workman's  face  may  not  be  over 
the  bottle  while  blowing.  As  soon  as  the  assay  has 
cooled,  100  c.  c.  of  normal  solution  are  added  by  means 
of  the  pipette,  and  the  bottle  is  put  into  a  japanned  tin 
case,  or  enveloped  in  a  cloth,  to  prevent  the  action  of  the 
daylight  on  the  silver  chloride,  which  might  slightly 
vitiate  the  result,  *and  the  stopper,  previously  dipped  in 
pure  water,  is  put  in.  The  bottle,  held  as  shown  in  the 
diagram,  is  briskly  shaken  for 
several  minutes,  which  causes  the 
precipitate  to  curdle,  and  settle 
rapidly,  leaving  the  liquid  per- 
fectly clear.  On  placing  the 
bottle  on  the  table,  to  allow  of 
the  settling,  a  brisk  to  and  fro 
circular  movement  is  given  to  it, 
so  as  to  wash  down  from  the 
sides  any  adhering  chloride.  When  the  liquid  is  quite 
clear,  the  stopper  is  removed  and  suspended  in  a  clamp, 
or  bracket,  so  that  the  moistened  part  may  touch  noth- 
ing. A  c.  c.  of  decime  salt  solution  is  poured  into  the 
bottle.  If,  immediately  or  after  a  few  seconds,  a  cloudi- 
ness is  perceptible  in  the  liquid,  it  is  evident  that  the 
normal  solution  is  weak,  because  100  c.  c.  of  it  have  not 
precipitated  1,000  of  silver.     The  liquid  must   be  again 


*This  precaution  will  be  unnecessary  if  the  room  is  illuminated  by 
windows  of  yellow  glass. 


64  ASSAYING   GOLD 

cleared  by  shaking,  and  another  c.  c.  of  decime  salt  solu- 
tion added,  and  so  on  until  no  further  cloud  is  produced. 
A  record  of  the  number  of  c  c.  of  decime  solution  used 
is  kept,  but  the  last  one  is  not  counted,  because  it  pro- 
duced no  effect,  and  the  one  before  the  last  was  probably 
not  all  required,  so  it  is  counted  as  a  half.  Supposing 
that  7  c.  c.  caused  precipitation,  but  the  8th  did  not; 
only  6  J  must  be  counted. 

It  now  appears  as  though  1,006 J  points  of  silver  had 
been  present  in  the  solution,  but  it  is  known  that  there 
were  but  1,000,  because  that  quantity  was  weighed;  the 
normal  solution  is  therefore  6 J  points  weak,  and  requires 
a  corresponding  addition  of  salt.  The  quantity  of  salt 
required  is  found  by  the  following: — 

Rule. — Multiply  the  weight  or  measure  of  salt  or 
saturated  solution  used  in  making  the  entire  quantity  of 
normal  solution  by  the  number  of  c.  c.  of  decime  salt 
solution  which  were  necessary  to  complete  precipitation, 
and  divide  by  1,000.  The  result  is  the  weight  or  measure 
of  the  required  addition. 

A.S  a  portion  of  the  normal  has  been  withdrawn  for 
the  test  and  for  making  the  decime  solution,  the  quan- 
tity thus  found  may  be  corrected  by  the  deduction  of  a 
corresponding  percentage;  but  it  is  not  worth  while,  un- 
less either  many  tests  have  been  made,  or  but  a  small 
quantity  of  normal  has  been  prepared,  for,  even  though 
the  addition  required  may  be  considerable,  it  is  evident, 
from  the  fact  that  the  normal  is  weak,  that  the  saturated 
solution  used  was  less  strong,  or  the  salt  less  pure,  than 
was  supposed,  so  that  the  .added  quantity  will  have  the 
same  deficiency  in  proportion.     If  dry  salt  was  used  in 


AND   SILVER   BULLION.  65 

« 

making  the  normal,  and  consequently  will  be  used  also 
in  the  correction,  the  required  quantity  should  be  dis- 
solved in  some  of  the  original  normal  poured  into  a 
beaker  for  that  purpose,  and  then  mixed  with  the  main 
stock,  the  beaker  being  rinsed  with  a  very  little  water 
and  that  also  added.  Another  test  must  then  be  made, 
and,  if  necessary,  another  correctioA. 

If  the  first  addition  of  1  c.  c.  of  decime  salt  solution 
produces  no  precipitate,  it  is  known  that  the  normal  is 
either  correct  or  too  strong.  To  ascertain  which,  add  2 
c.  c.  of  decime  silver  solution;  one  of  these  is  consumed 
in  neutralizing  the  c.  c.  of  decime  salt  previously  added, 
hence  only  one  is  counted.  Shake  down,  and  add 
another  c.  c.  of  decime  silver;  if  this  produces  no  cloud, 
the  normal  is  correct  within  at  most  a  point,  and  may  be 
accepted,  for  it  is  needless  to  make  it  perfect,  for  reasons 
which  will  appear  hereafter.  If  a  cloud  is  produced, 
shake  down  again,  and  continue  adding  decime  silver 
solution  and  shaking  down  until  the  last  added  c.  c. 
causes  no  cloudiness;  then,  as  with  the  salt,  reject  the 
last  c.  c.  and  half  of  the  preceding  one.  Supposing 
that,  in  all,  5  c.  c.  have  been  used;  we  reject  one  of  the 
first  two  added,  because  it  only  counteracted  the  c.  c.  of 
decime  salt  previously  added;  we  also  reject  the  last,  be- 
cause it  gave  no  precipitate,  and  the  one  before  the  last 
we  count  as  a  half  c.  c.  Thus  we  have  2J  c.  c-  of  decime 
silver  solution  which  were  necessary  to  complete  the  de- 
composition of  the  salt  in  100  c.  c.  of  the  normal.  Ap- 
parently only  997J  points  of  silver  were  dissolved,  but 
we  know  that  1,000  were  so;  consequently  tlie  normal  is 
2J  points  too  strong,  and  water  must  be  added.     The 


66  ASSAYING   GOLD 

quantity  of  water  required  is  found  by  the  following: — 

Rule. — Multiply  the  quantity,  by  weight  or  measure, 
of  water  used  in  making  the  entire  quantity  of  normal 
solution  by  the  number  of  c.  c.  of  decime  silver  solution 
which  were  necessary  to  complete  the  assay,  and  divide 
by  1,000.  The  result  is  the  quantity  of  water  to  be 
added  to  the  normal  solution.     Mix  thoroughly. 

A  correction  for  the  percentage  of  the  normal  which 
has  been  used  is  more  necessary  in  this  case;  still  it  is 
hardly  worth  the  trouble  of  making  it  because,  if  the 
error  of  the  normal  is  large,  a  second  rectification  will 
probably  be  required,  and  if  it  is  small,  the  difference 
will  not  be  perceived.  After  mixing,  test  again;  when 
the  normal  is  sufficiently  exact  make  a  new  decime  salt 
solution. 

Examples. — The  normal  solution  was  made  with  5 
flbs.  avoirdupois  of  saturated  solution,  and  a  test  assay  on 
pure  silver  required  8J  c.  c.  of  decime  salt  solution  to 
finish;  then,  5  times  8|  make  42.5,  and  this  divided  by 
1,000  gives  0.0425  lbs.  of  saturated  solution  to  be  added 
to  the  normal.  A  pound  avoirdupois  is  equal  to  7,000 
grains  troy,  and  multiplying  this  by  0.0425  we  have 
297.5  grains. 

Again,  the  normal  solution  was  made  with  189 J  lbs. 
of  water,  and  proves  to  be  too  strong,  a  test  assay  re- 
quiring b\  c.  c.  of  decime  silver  solution  to  finish;  then, 
189.5  multiplied  by  5.5  gives  1,042.25,  which,  divided  by 
1,000  gives  1.04  pounds  of  water  to  be  added. 

If  dry  salt  had  been  used,  or  if  the  saturated  solution 
or  the  water  had  been  measured  by  volume,  the  same 
kind  of  calculation  would  give  the  required  result  in 
terms  of  the  weight  or  measure  used. 


AND  SILVER  BULLION.  67 

When  the  normal  solution  is  within  about  a  point  of 
being  correct,  it  may  be  accepted,  perfect  accuracy  being 
needless  on  account  of  the  changes  of  volume  produced 
by  alterations  of  the  temperature,  for  which  a  correction 
must  be  made  as  hereafter  directed,  and  includes  any 
inaccuracy  in  the  standardizing;  for  the  present,  however, 
the  solution  will  be  supposed  to  be  exact. 

The  Assay. — For  the  sake  of  convenience,  a  c.  c.  of 
either  of  the  decime  solutions,  will  be  called  a  jpoint  of 
silver,  or,  a  point  of  salt,  as  the  case  may  be;  also  100 
c.  c.  of  the  normal  solution  will  be  called  a  thousand  of 
salt. 

One  thousand  of  salt  requires  1,000  of  silver,  and  such 
a  weight  of  the  bullion  is  taken  for  the  assay  as  con- 
tains, as  nearly  as  may  be,  1,000  of  silver.  This  being 
dissolved,  and  1,000  of  salt  added,  we  then  proceed,  by 
means  of  the  decime  solutions,  to  ascertain  how  many 
points  more  or  less  than  1,000  the  assay  con  tains- 
Knowing  the  weight  taken,  and  having  found  the  weight 
of  the  contained  silver,  it  is  easy  to  find  by  propor- 
tion what  weight  of  silver  1,000  of  the  bullion  contains, 
which  is  its  fineness. 

In  order  to  be  able  to  take  the  required  weight  of  the 
sample,  we  must  have  an  approximate  knowledge  of  its 
silver  fineness.  This  is  obtained  by  means  of  a  prelimi- 
nary assay  by  cupellation  and,  if  necessary,  parting.  As 
we  know  from  experience  that  there  is  a  certain  loss  of 
silver  in  the  cupellation,  we  add  to  the  result  of  the  pre- 
liminary assay  such  a  number  of  points  as  the  judgment 
may  dictate.  From  the  approximate  fineness  thus  ob- 
tained we  calculate  the  weight  which  must  be  taken  in 


DO  ASSAYING   GOLD 

order  that  the  assay  may  contain  nearly  1,000  of  silver; 
thus,  suppose  the  cupellation  (and  parting)  gave  a  silver 
fineness  of  .864,  and  we  add  3  points  for  loss,  making 
.867,  then,  as  867  are  to  1,000  so  are  1,000  to  1,153.4. 
and  we  weigh  off  1,154;  hence  the 

Rule. — Divide  1,000,000  by  the  number  of  points  of 
approximate  fineness ;  the  result  is  the  desired  weight  in 
points. 

Dissolve  that  quantity  of  the  sample  in  about  7  c  c. 
of  nitric  acid,  in  the  manner  directed  for  the  standard- 
izing of  the  normal  solution;  cool,  add  1,000  of  salt, 
shake  down  and  add  a  point  of  salt.  If  a  cloud  is  pro- 
duced, proceed  to  complete  the  assay  with  salt,  as  in  test- 
ing the  normal  solution,  keeping  a  record  of  the  number 
of  points  added,  finally  rejecting  the  last  and  half  of 
the  preceding  one.  Suppose  1,154  of  the  bullion  to  have 
been  taken,  and  that  3  points  of  salt  have  given  a  pre- 
cipitate, the  4th  none.  We  have  then  found  that  1,154 
points  of  the  bullion  contain  1,002J  points  of  silver. 
To  find  the  fineness,  we  take  the  proportion,  as  1,154  are 
to  1,002.5  so  are  1,000  to  869.7.  As  not  less  than  a 
point  is  usually  stamped  on  a  bar,  we  may  say  the  bullion 
is  .869  fine. 

If  the  first  added  point  of  salt  gives  no  precipitate, 
add  a  point  of  silver  to  neutralize  it,  shake  down  and 
add  another ;  if  this  produces  no  precipitate,  the  assumed 
fineness  was  correct;  if  otherwise,  proceed  to  finish  with 
silver  in  the  same  manner  as  with  salt;  then,  rejecting 
the  first  point  because  it  was  required  to  counteract  the 
point  of  salt,  and  the  last  because  it  gave  no  result,  also 
half  of  the  preceding  one  because  it  was  probably  only 


AND   SILVER  BULLION.  69 

required  in  part,  deduct  the  remainder  of  the  added 
points  from  1,000,  which  leaves  the  number  of  points 
in  the  assay.  If,  as.  before,  1,154  of  the  bullion  were 
taken,  and  pne  added  point  of  salt  gave  no  precipitate, 
and  4  successive  points  of  silver  gave  a  precipitate,  the 
6th  none,  then  it  is  known  that  1,154  of  the  bullion 
contain  998J  of  silvier,  and  as  1,154  are  to  998.5  so  are 
1,000  to  865.25,  or  the  bullion  is  .865  fine.  Hence,  to 
find  the  fineness,  the  following 

Rule. — Multiply  the  points  of  silver  found  by  1,000, 
and  divide  by  the  points  of  bullion  taken. 

Greater  exactitude  can  be  attained  by  finishing  with 
half  points,  but  for  ordinary  purposes  it  is  not  necessary. 
The  gold  fineness  of  the  bullion  is  found  in  the  prelimi- 
nary assay  by  cupellation  and  parting. 

It  is  better  to  finish  with  salt  than  with  silver,  so  the 
weight  of  bullion  taken  for  the  assay  should  be  such  as 
to  contain  a  little  more,  rather  than  less  than  1,000  of 
silver;  and  if  it  is  not  so,  and  is  found  to  contain  less,  a 
number  of  points  of  silver  may  be  added  at  once,  so  as 
to  make  more  than  1,000;  the  assay  is  then  finished  with 
salt.  An  account  must  be  kept  of  the  silver  and  salt 
added,  the  one  +,  the  other  — .  If  more  than  eight 
points  of  salt  or  silver  are  required  to  finish,  it  is  advis- 
able to  make  another  assay  on  the  basis  of  the  result 
found. 

The  last  trace  of  precipitate  is  somewhat  difiicult  to 
discern.  It  can  be  seen  best  by  looking  obliquely  up- 
ward through  the  liquid,  while  holding  the  bottle  toward 
the  light.  Another  help  is  to  have  a  black  background, 
for  which  a  black  felt  hat  answers.     The  writer  and  some 


70  ASSAYING  GOLD 

others  have  found  it  advantageous  to  have  the  assay  so- 
lution tinged  by  copper;  the  white  silver  chloride  shows 
very  plainly  in  the  blue  solution.  An  experienced  as- 
sayer,  on  observing  that  the  first  added  point  of  salt 
causes  a  considerable  precipitate  immediately,  will  add 
several  more  points  before  shaking  down,  being,  able  to 
judge  about  how  many  will  be  required;  he  can  also  tell, 
almost  with  certainty,  when  another  point  will  be  with- 
out effect. 

In  case  the  furnace  is  not  fired,  a  preliminary  assay 
may  be  made  by  means  of  the  blowpipe.  It  is  not  neces- 
sary that  any  special  weight  be  taken,  therefore  select  a 
piece  of  the  bullion  which  may  weigh  about  100,  more  or 
less;  weigh  it,  cupel  it  with  lead  before  the  blowpipe 
flame,  not  allowing  the  flame  to  touch  the  metal,  but 
heating  the  cupel  around  it  by  directing  the  point  first  on 
one  side  and  then  on  another;  weigh  the  bead,  part,  and 
weigh  the  gold  if  there  is  much;  then,  as  the  weight  of 
the  silver  is  to  that  of  the  assay,  so  is  1,000  to  the  weight 
of  the  bullion  to  be  taken  for  the  volumetric  assay,  to 
which  a  few  points  may  be  added  for  the  loss,  which  is 
likely  to  be  greater,  at  least  in  inexperienced  hands,  than 
in  the  muffle.  The  gold  may  be  calculated  for  1,000  on 
the  same  principle,  but  it  may  be  better  to  dissolve  1,000 
of  the  bullion  in  nitric  acid,  and  weigh  the  gold  from 
that,  the  only  difficulty  being  that  it  is  likely  to  be  in 
finer  powder  than  when  parted  from  a  bead  which  has 
been  purified  from  base  metal  by  cupellation. 

An  excellent  preliminary,  and  even  an?accurate  assay, 
may  be  made  by  means  of   a    Mohr  burette.*     Dissolve 
*For  a  description  of  this,  and  its  use,  see  Part  3d. 


AND  SILVER   BULLION.  71 

1,000  of  the  bullion  as  usual.  Charge  the  burette  very 
accurately  with  normal  solution,  and  run  that  into  the 
assay  bottle,  first  in  larger,  then  in  smaller  quantities, 
finally  drop  by  drop,  shaking  down  each  time,  until  the 
Jast  drop  or  two  produces  no  precipitate.  The  value  of 
a  drop  may  be  ascertained  by  noting  how  many  drops 
lower  the  float  1  c.  c.  The  last  addition,  which  produces 
no  precipitate,  is  not  counted,  and  the  preceding  is 
counted  for  half  its  value.  The  burette  should  be  read 
after  each  addition  toward  the  end.  It  should  be  of  100 
c.  c.  capacity,  graduated  to  tenths,  and  furnished  with  a 
float.  If,  by  accident,  an  excess  of  salt  solution  is  run  in, 
add  ten  or  more  points  of  decime  silver  solution,  making 
a  note  of  it ;  and  then  finish  with  salt.  If  preferred,  the 
assay  may  be  finished  with  decime  salt  solution  from  a 
second  burette,  or  from  the  small  pipette,  but  with  care 
this  will  not  be  necessary,  as  the  normal  can  be  measured 
to  less  than  a  point.  The  number  of  c,  c*  necessary  for 
complete  precipitation  is  the  fineness,  provided  no  addi- 
tion of  decime  silver  has  been  made;  otherwise  that  must 
be  deducted.  Special  care  must  be  taken  that  no  air  re- 
mains in  the  jet  of  the  burette  when  charged,  to  which 
end  it  is  best  to  partly  charge  it  from  below,  by  suction, 
and  then  fix  it  in  the  stand  and  fill  it  from  above. 

Correcting  the  Assay.— It  has  thus  far  been  sup- 
posed that  the  normal  solution  was  accurately  standard- 
ized so  that  100  c.  c.  would  exactly  precipitate  1,000  of 
silver.  In  order  that  this  may  be  the  case,  it  must  not 
only  have  been  made  of  the  correct  strength,  but  it  must 
always  be  used  at  the  same  temperature.     This  cannot 

•  This  should  have  been  written  tenths  of  c.  c. 


72  ASSAYING  GOLD 

well  be.  For  this  reason  a  check  assay  is  made,  on  pure 
silver,  with  each  set  of  bullion  assays,  a  number  of  which 
can  be  conducted  at  the  same  time,  and  are  corrected  ac- 
cording to  the  error  found,  whether  that  is  caused  by  ex- 
pansion or  contraction  of  the  solutions,  owing  to  a  change 
of  the  temperature,  or  from  inaccurate  standardizing. 

The  result  of  an  assay  of  pure  silver  should  be  1,000 
fine ;  if  it  ^ives  more  or  less,  the  assay  of  each  sample  of 
bullion  must  be  corrected  in  proportion  to  its  fineness. 
This  is  arrived  at  with  sufficient  exactness  by  adding  to, 
or  subtracting  from,  the  number  of  points  found  in  the 
^assay,  the  amount  of  the  error  of  the  check,  before  calcu- 
lating the  fineness  of  the  bullion.  Thus:  if  the  result  of 
the  check  is  2\  points  aoove  1,000,  that  quantity  must  be 
deducted;  if  below,  added.  Suppose  the  check  was  2 J 
points  high,  and  1,154  of  bullion  gave  1,005^;  we  deduct 
2 J  from  that,  leaving  1,003,  from  which  we  then  calcu- 
late the  fineness,  which  is  870.  If  the  check  had  been 
IJ  low,  we  should  have  added  IJ,  making  1,007  in  1,154, 
and  the  fineness  would  have  been  .873. 

General  Remarks  on  the  Humid  Assay. — Silver 
bullion  from  retorted  amalgam  is  said  to  sometimes  con- 
tain mercury.  The  presence  of  mercury  in  sensible 
quantity  impairs  the  accuracy  of  the  humid  assay  as 
described.  To  overcome  this  difficulty,  add  to  the  dis- 
solved metal  in  the  bottle  10  grammes  (154.3  grains)  of 
sodium  acetate,  and  then  proceed  as  usual.  Mercury 
may  be  detected  in  the  assay  by  the  silver  chloride  re- 
maining white  when  exposed  to  the  daylight ;  in  the 
absence  of  mercury  it  quickly  assumes  a  purplish  hue, 
finally  becoming  almost  black.     If  the  presence  of  mer- 


AND   SILVER   BULLION.  73 

cury  is  thus  detected  in  an  assay,  a  new  assay  must  be 
made,  adding  the  sodium  acetate  before  the  salt.  If  the 
bullion  is  suspected  of  containing  mercury,  the  acetate 
may  be  used,  as  it  will  do  no  harm  in  any  case;  or,  a 
little  of  the  bullion  may  be  dissolved  in  nitric  acid,  the 
silver  precipitated  by  salt,  and  the  precipitate  exposed  to 
the  light.  Direct  sunlight  acts  very  quickly.  If  the 
precipitate  becomes  discolored,  it  contains  no  mercury. 

If  any  difficulty  is  found  in  obtaining  a  clear  solution 
of  the  assay  in  the  bottle,  it  may  be  boiled  with  nitric 
acid  in  a  mattrass,  and  afterwards  transferred  to  the 
assay  bottle;  the  mattrass  must  be  rinsed  thrice  with  a 
little  distilled  water,  and  that  added  to  the  solution  in 
the  bottle.  An  addition  of  sulphuric  acid  is  sometimes 
useful.     The  acid  must  be  pure. 

If  a  number  of  assays  are  to  be  made,  they  may  all 
be  dissolved  at  once,  and  each  bottle  dosed  with  1,000 
of  salt,  shaken  down,  and  then  a  point  of  salt  poured 
into  each,  and  so  on,  saving  time.*  When  the  assays 
are  finished,  the  bottles  should  be  washed  thrice  with 
pure  water.  Care  must  be  taken,  especially  in  warm 
weather,  not  to  allow  the  perspiration  to  come  in  con- 
tact with  the  liquids  or  with  the  interior  of  the  vessels, 
because  it  contains  salt.  Salt  in  the  water  used  for 
making  the  normal  solution  is  not  injurious,  but  if  there 
is  much,  it  may  be  allowed  for.  The  decime  salt  solu- 
tion should  be  made  with  pure  water.  The  nitric  acid 
used  must  not  show  the  slightest  turbidity  when  pure 

*Sets  of  bottles,  with  pointed  stoppers,  may  be  bought  at  the 
dealers'.  Also  an  apparatus  mounted  on  springs  for  shaking  a  number 
at  once. 


6 


74  ASSAYING   GOLD 

silver  is  dissolved  in  it,  nor  on  the  addition  of  salt,  so 
that  the  regenerated  parting  acid  hereafter  mentioned 
is  not  suitable  for  the  humid  assay.  That  sold  in  bottles 
marked  C.  P.  (chemically  pure)  requires  to  be  diluted. 

In  large  establishments,  the  normal  solution  is  kept 
in  an  elevated  tank,  from  which  a  fixed  pipette  is  filled 
by  a  syphon.  For  a  description  of  various  apparatus 
and  methods,  the  reader  is  referred  to  "  Mitchell's  Man- 
ual," and  to  "Rickett's  Notes  on  Assaying." 

It  is  not  essential  that  the  normal  pipette  shall  contain 
100  c.  c.  It  may  be  much  smaller,  and  the  solution  pro- 
portionately stronger,  if  the  neck  is  narrowed  in  similar 
ratio  so  that  the  measurement  may  be  more  exact.  The 
writer  has  made  and  used  pipettes  of  which  that  for  the 
normal  solution  was  formed  from  the  barrel  of  a  small 
glass  syringe,  the  original  nozzle  being  utilized  as  the 
neck,  on  which  the  mark  was  made  by  filing,  and  a 
delivery  jet  formed  on  the  other  end  by  the  aid  of  the 
blowpipe.  It  contained  less  than  10  c.  c,  or  about  145 
grains  of  water.  The  auxiliary  pipettes  were  made 
from  glass  tubes,  with  neck  and  beak  like  the  normal. 
(The  decinie  solution  pipettes  are  usually  made  with  a 
beak,  but  not  a  neck.)  These  were  of  one- tenth  the 
capacity  of  the  normal,  instead  of  ^hr-  as  is  usual  (but 
which  would  have  been  inconveniently  small  in  this 
case),  and  to  compensate  this,  centime,  instead  of  decime 
solutions  were  used.  The  orifices  were  all  very  narrow, 
and  the  pipettes  were  charged  by  sucking,  and  emptied 
by  blowing.  The  larger  pipette  not  corresponding  to 
any  standard  measure,  it  was  filled  to  the  mark  with 
water,  and  emptied  into  a  graduated  cylinder  as  many 


AND   SILVER   BULLION.  7S 

times  as  was  necessary  to  make  a  definite  measure,  which 
Afforded  a  basis  for  making  any  required  quantity  of  a 
normal  solution  of  which  each  pipetteful  should  contain 
1,000  of  salt.  To  test  the  accuracy  of  this  apparatus, 
four  separate  pipettefuls  of  water  were  weighed  on  a 
delicate  balance ;  they  agreed  two  and  two,  the  difference 
between  the  pairs  being  w^jj  grain,  which  was  closer  than 
was  necessary.  Crucial  test  assays,  the  one  finished  with 
salt,  the  other  with  silver,  agreed  within  a  half  point. 
This  apparatus  is  far  better  to  work  with  by  hand  than 
the  larger  one.  It  is  necessary  to  add  some  water  to  the 
assay  to  furnish  the  requisite  volume  of  liquid  for  the 
settling.  A  10  c.  c.  pipette  can  be  bought  for  a  trifle, 
and  the  small  ones  will  be  the  same  as  those  ordinarily 
used  if  centime  instead  of  decime  solutions  are  employed. 

The  researches  of  G.  J.  Mulder  have  shown  that,  in 
the  humid  assay  as  described,  a  point  may  be  reached  at 
which  either  salt  or  silver  will  give  a  precipitate,  and  it 
has  been  asserted  that,  in  a  warm  climate,  this  may  give 
rise  to  an  error  of  several  points ;  there  is,  however,  no 
danger  if  matters  are  so  managed  as  that  the  check  and 
the  bullion  assay  are  both  finished  in  the  same  manner, 
preferably  with  salt,  which  gives  the  better  clearance  of 
the  liquid. 

Recovery  of  Silver. — The  assays  being  finished,  the 
bottles  are  emptied  into  an  earthern  jar,  and  when  a  suf- 
ficient quantity  of  silver  chloride  has  accumulated,  the 
liquid  is  poured  off  The  chloride  is  washed,  and  some 
pieces  of  iron  or  zinc  and  very  dilute  sulphuric  acid  are 
added.  In  a  few  days  the  silver  is  reduced  to  the  metal- 
lic state  in  the  form  of  a  gray  powder.     This  is  washed. 


76  ASSAYING   GOLD 

dried,  and  melted  in  a  black-Jead  crucible  with  some 
borax.  As  this  silver  will  contain  all  the  gold  which 
was  in  the  assays,  it  is  not  suitable  for  the  purpose  of 
inquartation,  nor  for  humid  assay  checks. 

Preparation  OF  Pure  Silver.— Dissolve  the  thoroughly 
washed  chloride  from  the  humid  assays,  or  from  the  part- 
ing acid  treated  with  salt  or  hydrochloric  acid,  in  warm 
strong  brine  of  common  salt.  Filter  the  solution  into  a 
porcelain  or  glass  dish  (a  wash  basin  will  serve).  In  the 
middle  of  the  dish  place  a  smaller  porous  vessel  contain- 
ing salt  brine,  with  a  very  little  nitric  acid.  (For  a  por- 
ous vessel  a  hessian  crucible,  which  has  stood  full  of  water 
until  soaked  through,  will  answer.)  Cut  a  piece  of  sheet 
copper  of  such  a  size  as  to  form  a  cylinder  which  can 
be  placed  in  the  porous  vessel,  not|touchingthe  side.  From 
one  edge  of  the  copper  cut  a  narrow  strip,  but  not  en  - 
tirely  off,  leaving  it  connected  to  the  sheet.  Take  a  strip 
of  test  silver  long  enough  to  form  a  ring  around,  but  not 
touching  the  porous  vessel,  and  from  the  edge  cut  a  strip 
partly  off,  as  with  the  copper.  Clean  the  copper  by  im- 
mersion for  a  few  minutes  in  dilute  nitric  acid  and  then  in 
water.  Connect  the  copper  and  the  silver  by  soldering 
the  ends  of  the  strips,  or  by  folding  them  together.  Bend 
the  plates  suitably  and  place  the  copper  in  the  porous 
vessel,  the  silver  in  the  basin  containing  the  solution  of 
silver  choloride,  the  connecting  strips  forming  an  arch 
above  the  liquids.  Keep  the  whole  warm,  and,  if  neces- 
sary, renew  the  solution  in  the  porous  vessel,  or  add  a  little 
acid  from  time  to  time. 

Pure  silver  in  the  form  of  small  white  crystals  will  be 
deposited  on  the  silver  plate.     Iron  or  zinc  in  the  porous 


AND   SILVER   BULLION.  77 

cell  would  work  faster  than  copper,  but  would  not  give 
pure  silver,  as  they  would  cause  the  precipitation  of  any 
trace  of  lead,  copper,  etc.  which  might  be  present,  as  well 
as  of  the  silver.  If  pure  silver  for  a  plate  cannot  be  had, 
a  piece  of  coke  may  be  used  instead,  being  connected  with 
the  copper  by  means  of  a  copper  wire  soldered  to  that, 
and  wound  around  a  notch  cut  in  the  coke  above  the 
liquid. 

The  precipitated  silver  should  be  washed,  first  with  hot 
water  containing  some  salt  and  a  little  hydrochloric  acid, 
and  then  with  pure  hot  water  until  that  gives  no  precip- 
itate on  addition  of  solution  of  silver  nitrate.  If  des- 
tined to  be  melted,  the  silver  may  be  dried  by  evapora- 
tion after  draining;  otherwise  it  should  be  first  pressed 
between  sheets  of  filter  paper,  and  then  dried  by  heat, 
and  kept  in  a  stoppered  bottle. 

The  dried  silver  may  be  melted  in  a  clean  black-lead 
pot,  or  in  a  clay  crucible  lined  with  charcoal,  a  little  bo- 
rax being  added,  and  cast  into  narrow  bars  like  those  of 
solder.  The  bars  may  be  cut  into  chips  by  the  chisel,  or 
laminated  by  the  rolling  mill,  after  being  reduced  to  a 
thickness  of  about  J  inch  by  hammer  and  anvil,  be- 
ing cut  into  suitable  lengths,  and  annealed  whenever 
necessary  for  the  rolling.  The  filter,  through  which  the 
solution  of  silver  chloride  in  brine  was  passed,  may  be 
dried,  dressed  with  litharge  and  borax,  smelted  in  a  cruci- 
ble, and  the  resulting  lead  button  cupelled  for  recovery  of 
gold.  To  line  a  crucible  with  charcoal,  beat  in,  little  by 
little,  finely  ground  and  slightly  moistened  charcoal  until 
the  pot  is  filled,  then  scoop  out  the  central  portion,  leaving 
a  lining  about  half  an  inch  thick,  more  or  less.  Smooth 
the  interior  by  means  of  a  glass  rod  or  a  test-tube. 


78  ASSAYING  GOLD 

Recovery  of  Acid. — The  nitric  acid  used  in  the  humi^ 
assays  is  so  far  saturated  with  silver  that  its  recovery 
would  scarcely  be  profitable,  especially  as  it  is  contami- 
nated by  sodium  nitrate,  resulting  from  the  salt  used  ii^ 
the  assay.  That  which  has  been  used  for  parting,  how- 
ever, contains  but  little  silver  in  proportion,  yet  it  is 
usually  wasted,  because  salt  is  used  to  precipitate  the 
silver  for  recovery  of  that,  and  the  acid  is  rendered  unfit 
for  further  use  in  assaying.  The  acid,  as  well  as  the 
silver,  may  be  recovered  in  a  suitable  condition  for  reuse* 
the  one  for  parting,  the  other  for  inquartation,  by  pro- 
ceeding as  follows: — 

After  standing  undisturbed  for  several  days,  to  allow 
any  suspended  gold  to  settle,  the  greater  part  of  the  acid 
is  carefully  poured  or  syphoned  into  a  suitable  vessel  of 
glass  or  porcelain,  all  sediment  being  left  behind.  Hy- 
drochloric acid  is  then  added,  little  by  little,  to  precipitate 
the  silver  as  chloride,  with  great  care  not  to  use  an  ex- 
cess. The  liquid  is  briskly  stirred  by  means  of  a  glass 
rod,  and  then  allowed  to  remain  undisturbed  until  the 
silver  chloride  has  settled ;  or,  a  little  of  it  may  be  taken 
in  a  bottle,  cleared  by  shaking  as  in  the  humid  assay, 
and  tested  with  a  drop  of  hydrochloric  acid.  It  is  not 
best  to  attempt  the  complete  precipitation  of  the  silver, 
as  a  small  quantity  remaining  in  solution  will  not  be 
injurious,  while  an  excess  of  hydrochloric  acid  will; 
should  the  latter  be  accidentally  added,  the  error  can  be 
rectified  by  means  of  some  silver  solution,  for  which  pur- 
pose a  portion  of  the  original  should  have  been  set  aside. 
When  a  drop  of  hydrochloric  acid  produces  only  a  very 
slight  cloud,  the  liquid  is  allowed  to  stand  undisturbe(i 
for  24  hours,  covered  to  exclude  light  and  dust.     It  is 


AND   SILVER   BULLION.  79 

then  filtered  through  fibrous  asbestus,  ground  bottle 
glass,  or  quartz,  until  it  is  perfectly  bright.  It  should 
now  give  a  slight,  yet  distinct,  precipitate  on  addition  of 
dilute  hydrochloric  acid  to  a  little  in  a  test-tube,  but  none 
with  solution  of  silver  nitiate.  The  hydrochloric  acid 
produces  nothing  but  water  and  silver  chloride,  and  the 
recovered  acid  is  as  good  as  any  for  the  purpose  of  part- 
ing, but  should  not  be  used  for  the  humid  assay,  because 
a  trace  of  silver  is  left  in  it  as  a  safeguard  against  the 
presence  of  chlorine.  The  presence  of  a  very  little  copper 
resulting  from  previous  partings  and  not  removed  by  this 
treatment  does  no  harm. 

This  method  was  introduced  by  the  writer  in  1864,  in 
an  off^ice  where  a  large  business  was  done  in  gold  bullion. 
It  was  used  for  years  with  perfect  success  and  consider- 
able econom3^  Ordinary  commercial  nitric  acid,  costing 
about  one-tenth  as  much  as  the  c.  p.  but  often  containing 
a  little  chlorine,  may  be  rectified  by  the  addition  of  a 
sliorht  excess  of  silver  nitrate,  and  used  with  perfect 
safety  for  parting. 

The  silver  chloride  precipitated  from  the  parting  acid 
is  treated  as  described  under  Recovery  of  Silver,  and  is 
again  used  for  inquartation  of  gold  assays.  It  must  con- 
tain no  gold,  and  will  contain  none  if  the  preceding  di- 
rections are  followed. 


CONCLUSION. 

AssAYERS  of  bullion  who  work  for  custom  must  remem- 
ber that  they  are  responsible  for  the  value  of  a  bar  as 
stamped  by  them.     If  any  U.  S.  Mint,  or  any  private 


80  CONCLUSION. 

office  in  good  standing,  finds  the  value  to  be  less,  a  recla- 
mation is  made  by,  or  on  behalf  of,  the  buyer  of  the  bar, 
which  the  assayer  on  whose  stamp  it  was  bought  must 
pay  if  he  wishes  his  stamp  to  pass  in  the  market.  It 
matters  not  that  his  assay  may  have  been  correct;  the 
purchaser  knows  nothing  of  that.  If  the  chips  have 
been  preserved,  as  they  should  be,  it  may,  in  some  cases, 
be  possible  to  bring  the  fault  home  to  the  office  in  which 
it  was  committed,  and  the  first  assayer,  if  right,  may  re- 
cover his  money;  but  this  will  hardly  avail  with  the 
mint,  perhaps  because  "  the  King  can  do  no  wrong."  The 
system  pursued  in  the  mints  is  such  as  to  render  mistakes 
almost,  though  not  quite,  impossible.  An  instance  is 
within  the  knowledge  of  the  writer  in  which  a  reclama- 
tion was  made  on  a  mint  certificate.  The  error  was 
proved  to  have  been  made  in  the  mint,  beyond  reasonable 
doubt;  but  the  private  assayer  had  to  suffer  the  loss.  It 
is  needless  to  say  that  if  a  bar  is  stamped  too  low,  no 
complaint  is  usually  made  by  the  purchaser,  though  the 
fact,  if  known  to  the  seller,  might  lead  to  a  reclamation 
on  his  part,  and  would  certainly  injure  the  reputation  of 
the  assayer.  The  inference  to  be  drawn  from  these  re- 
marks is  obvious. 


PART    THRKE 


PART  III. 

MANIPULATION,    ETC. 


A  FILTER  must  be  circular  in  order  that,  when  placed 
in  a  funnel,  the  edge  may  be  even.  The  edge  must  not 
extend  beyond  that  of  the  funnel. 

To  cut  a  filter  to  fit  a  funnel,  fold  the  paper  twice  in 

diametrically  opposite  directions ;  place  it  on  a  table ;  put 

the  point  of  a  pair  of  pencil  compasses  close  to,  not  on, 

the  corner:  With  a  little  less  than  the  diameter  of  the 

funnel  between  the  points  of  the  compasses,  describe  an 

arc  of  a  circle  on  the  folded  paper.     Cut  with  scissors  to 

the  mark.     Or,  invert  the  funnel  upon  the  folded  paper, 

the  rim  at  the  corner;  look  down  through  the  stem  and 

see  the  edge  of  the  paper  passing  through  the  center  of 

the  funnel.     Make  a  mark  on  the  paper  where  the  rim  of 

the  funnel  intersects  the  edge.     Do  likewise  on  the  other 

edge  and  again  in  the  middle  and  at  as  many  points  as 

may  be  chosen,  marking  the  paper  at  a  distance  from  the 

corner  equal  to  the  funnel's  diameter.     Cut  a  little  within 

the  marks.     Or,  fold  the  paper  three  or  four  times;  cut 

straight  across  at  a  distance  from  the  corner  equal  to  the 

diameter  of  the  required  filter,  then  trim  to  an  arc  of  a 

circle.     Open  the  twice  folded  paper  so  that  it  shall  form 

a  cone  having  one  thickness  on  the  one  side  and  three  on 

the  other. 
(83 


84  ASSAYING, 

Place  the  cone  in  a  funnel;  hold  it  with  the  thumb  in- 
side, and  the  fingers  outside,  and  wet  the  paper  by  a  jet 
from  the  wash-bottle.  The  filter  should  fit  closely  to  the 
funnel  all  over  except  at  the  point,  but  especially  at  the 
rim,  which  should  be  air-tight.  Press  the  folded  edges 
with  the  rounded  end  of  a  glass  rod,  a  test-tube,  or  the 
thumb  nail. 

The  size  of  a  filter  should  be  adapted  to  the  bulk  of 
the  precipitate  when  that  is  wanted,  but  when  a  large 
volume  of  liquid  is  to  be  filtered  simpl}^  to  clear  it,  a  large 
filter  is  the  more  suitable.  Filters  already  cut  to  a  circle 
and  of  various  sizes  and  qualities  can  be  bought.  For 
solubility  assays  of  roasted  ore,  and  wet  copper  assays, 
gray  paper  answers  and  works  fast;  for  lead  and  zinc 
assays,  a  finer  quality  is  more  suitable. 

In  order  that  a  filter  may  fit  properly,  the  outline  of 
the  funnel,  except  the  neck,  viewed  sideways  must  form 
a  triangle  with  three  equal  straight  sides.  The  worst 
funnel  for  this  purpose  is  one  that  is  vase  shaped;  the 
side  and  the  neck  should  form  an  obtuse  but  clearly  de- 
fined angle,  not  a  curve. 

In  filtering,  fill  the  filter  often,  not  waiting  for  it  to 
drain.  In  washing  the  substance  on  the  filter,  and  the 
filter  itself,  let  it  drain  before  each  fresh  addition  of  water.* 
If  the  quantity  of  the  washings  is  immaterial,  it  is  best 
to  quite  fill  the  filter;  otherwise,  direct  the  stream  from 
the  wash-bottle  onto  all  parts  in  succession,  especially 
around  the  rim,  which  should  never  be  found  stained  with 
the  filtered  liquid  when  dried.  The  matter  on  the  filter 
may  generally  be  stirred  up  by  the  stream,  with  advantage 

*There  are  some  exceptions  to  this,  as  in  filtering  and  washing  some 
sulphides  which  must  be  kept  covered  to  prevent  access  of  air. 


MANIPULATION,    ETC.  85 

to  the  washing.  A  bulky  gelatinous  precipitate  may  be 
carefully  stirred  with  the  rounded  end  of  a  glass  rod.  At 
last,  if  the  precipitate  is  to  be  used,  wash  it  down  into 
the  point  of  the  filter.  Hereafter,  to  save  time  and  labor, 
a  precipitate  will  often  be  designated  by  the  sign  p.  p. 

It  is  generally  best  to  let  a  p.  p.  settle  before  filtering; 
then  filter  the  liquid  first,  as  far  as  practicable.  In  some 
cases  water  is  added  to  the  p.  p.,  stirred,  and  sometimes 
boiled  and  again  settled  and  filtered  off,  even  several 
times.  Finally,  allow  the  p.  p.  to  pass  onto  the  filter, 
washing  it  cleanly  from  the  vessel  by  a  jet  of  water, 
aided  if  necessary  by  a  brush  formed  of  a  clipped  feather. 
As  a  general  rule,  in  pouring  from  a  vessel  hold  a  glass 
rod  to  the  lip,  and  let  the  fluid  run  down  it  and  against 
the  side  of  the  filter  or  other  receiver. 

The  liquid  from  the  filter  (filtrate)  must  not  be  al- 
lowed to  fall  splashing  into  the  receiving  vessel,  but  should 
trickle  down  its  side.  Even  if  the  filtrate  is  not  required, 
a  neat  workman  will  not  have  it  splashed  about  the  table. 

There  are  several  ways  of  ascertaining  when  the  wash- 
ing of  a  p.  p.  is  completed.  If  the  filtrate  was  acid,  the 
washings  must  cease  to  redden  blued  litmus  paper:  if 
alkaline,  they  must  not  discharge  the  color  of  reddened 
litmus  paper.  If  the  water  used  be  pure,  a  drop  from  the 
filter,  evaporated  on  a  piece  of  glass,  should  leave  no  film, 
or  only  a  slight  speck. 

To  dry  a  p.  p.  first  let  it  be  well  drained,  which  may 
be  aided  by  i-emoving  the  triple  side  of  the  filter  from  con- 
tact with  the  funnel,  and  pressing  it  slightly  against  the 
opposite  side,  or  in  some  cases,  by  sucking  the  stem  of  the 
funnel,  but  not  too  forcibly  lest  the  paper  be  ruptured. 


86  ASSAYING, 

The  filter,  with  the  p.  p.,  may  be  carefully  removed  from 
the  funnel,  unfolded,  and  laid  on  a  waroa  surface,  better 
with  several  thicknesses  of  paper  under  it.  Special  ab- 
sorbent tiles  are  also  used.  Or  the  filter  with  its  contents 
may  be  dried  in  the  funnel,  that  being  placed  in  the  upper 
end  of  a  conical  tube  standing  on  a  sand-bath.  The 
drying  should  be  continued  until  two  weighings  after 
thorough  cooling  have  given  the  same  result. 

To  remove  a  dried  p.  p.  from  a  filter,  invert  that  on  a 
sheet  of  glazed  paper,  and  manipulate  it  with  the  fingers 
to  loosen  the  p.  p.  Scrape  it  with  a  wooden  or  horn  spatula ; 
double  it  and  rub  the  surfaces  together;  lay  it  fiat  and 
brush  it  with  a  rather  hard  brush,  etc.,  according  to 
circumstances. 

To  use  a  Mohr  burette  (see  wet  copper  assays),  fix  it  in 
a  vertical  position.  In  reading  it,  if  there  is  no  fioat,  the 
middle  of  the  concave  surface  of  the  liquid  is  the  indi- 
cator. The  eye  must  be  level  with  the  mark.  With  a 
float,  the  mark  around  that  is  the  indicator,  and  the  eye 
must  be  level  with  it,  so  that  it  appears  as  a  line,  not 
an  oval  ring.  In  charging  the  burette,  first  fill  it,  and 
see  that  no  air  bubbles  remain;  then,  by  compressing  the 
pinch-cock,  which  opens  it,  allow  the  liquid  to  escape 
into  a  vessel  bineath,  until  all  air  is  expelled  from  the  neck, 
and  then  refill  and  again  let  the  liquid  fiow  until  the  indi- 
cator is  exactly  coincident  with  the  upper  mark.  It  is 
then  ready  for  use. 

A  draught  place  should  be  provided  in  which 'acids 
may  be  boiled  and  hydrogen  sulphide  used  while  the 
fumes  are  conducted  away  by  a  flue.  Such  a  closet  is 
conveniently  made  by  fitting  a  box  on  the  outer  side  of 


MANIPULATION,  ETC.  87 

the  lower  half  of  a  wiadow,  so  that  the  lower  sash  forms 
a  front  which  can  be  opened  or  closed,  and  through 
which  the  progress  of  the  work  may  be  observed.  It  is 
still  better  if  the  back  be  glazed  also.  In  the  top  or  roof 
of  the  closet  is  a  small  wooden  flue  which,  if  convenient, 
may  be  connected  with  a  chimney.  Within  the  closet 
the  coal-oil  stove,  lamps,  etc.,  are  placed. 

Hydrogen  sulphide  is  a  gas  which  has  the  odor  of  rotten 
eggs.  It  is  produced  by  the  action  of  dilute  sulphuric 
acid  on  iron  protosulphide,  which  may  b3  made  by  melt- 
ing iron  filings  or  borings  with  sulphur,  or  may  be  bought. 
The  gas  is  conducted,  by  rubber  and  glass  tubing,  into 
water  to  wash  it,  and  then  into  the  beaker  or  other  vessel 
containing  the  liquid  treated.  It  is  used  in  certain  wet 
assays  to  precipitate  certain  metals  from  solution.  Va- 
rious kinds  of  apparatus  for  its  production  can  be  bought. 
For  all  the  purposes  of  this  book  an  eight-ounce  gener- 
ator will  suffice. 

Wash  all  vessels  after  use.  Balls  of  wet  paper  are 
useful  for  cleaning  the  interior  of  mattrasses,  etc.  Test 
tubes  sometimes  require  a  swab  on  a  slip  of  wood,  or 
a  test-tube  brush.  To  rinse  a  mattrass,  flask,  bottle,  or 
tube,  put  some  water  in  it,  stop  the  mouth  with  the 
thumb,  invert  the  vessel,  shake  it  so  as  to  wash  all  matter 
down  to  the  mouth;  then  remove  the  thumb.  Warm 
water  with  a  little  hydrochloric  acid  will  remove  iron  ox- 
ide and  many  other  residues.  Vessels  which  are  to  be 
used  for  parting,  for  the  humid  assay  of  silver,  or  for  any 
other  purpose  in  which  a  trace  of  a  chloride  or  chlorine 
would  be  objectionable,  must  be  rinsed  three  times  with 
pure  water.     Vessels  which  have  been   used  in  the  new 


88  ASSAYING. 

copper  assay,  etc.,  with  potassiutii  zanthate,  are  best 
cleaned  by  a  solution  of  potassium  cyanide  followed  by 
water.  The  clippings  of  filter  paper  are  useful  for  drying 
glassware. 

The  motto  of  a  work-shop  should  be,  "  A  job  is  not, 
finished  until  everything  is  put  in  order." 

Note. — Becker's  assay  balance  No.  5  is  strong  enough  for  th© 
weighing  of  most  of  the  wet  assays,  while  also  delicate  enough  for  that 
of  beads  from  gold  and  silver  ores.  Lead  and  copper,  etc.,  buttons  may 
be  weighed  on  the  pulp  scales. 


LEAD   ORES.  89 


LEAD    ORES. 


Fire  Assay. — All  lead  ores  can  be  assayed  b}^  melting 
with  soda,  borax,  iron,  and  carbon.  There  is  always  a 
loss  of  lead  in  the  fire  assay.  Many  of  our  lead  ores 
contain  copper  and  zinc,  and  if  sulphur  is  absent,  the 
copper,  or  some  of  it,  will  be  got  with  the  lead,  and  zinc 
will  largely  increase  the  loss. 

It  is  therefore  best,  for  those  not  well  acquainted  with 
the  different  ores,  to  convert  all  kinds  into  one  class,  to 
a  certain  extent,  by  an  addition  of  sulphur,  unless  it  is 
evident  that  sulphur  is  present  in  sufficient  quantity  to 
combine  with  all  the  copper  and  zinc  which  the  ore  may 
contain.  The  following  prescription,  slightly  varied  as 
to  the  proportions  of  soda  and  borax,  and  in  some  cases 
^with  an  addition  of  glass,  to  suit  the  different  gangues 
(see  Part  I,  Article  "Materials")  will  give  results  suffi- 
ciently accurate  for  many  purposes  of  metallurgy  and 
prospecting.  The  ore  should  be  passed  through  a  sieve 
of  40  meshes  to  the  running  inch. 

Ore 1  part 

Soda 1     " 

Dried  Borax 1     " 

Flour I    " 

Sulphur 1     " 

The  sulphur  may  be  omitted  if  the  ore  contains  no 
7 


90  ASSAYING 

metallic  nor  oxidized  copper,  as  blue  or  green  carbonate, 
black  or  red  oxide,  and  no  zinc  except  in  the  form  of 
blende;  also  when  the  ore  contains  any  considerable 
quantity  of  sulphur  in  the  form  of  galena  or  pyrites,  but 
zinc  blende  forms  no  exception,  requiring  all  its  own 
sulphur.  Mix  and  place  in  a  crucible;  cover  with  salt, 
and  some  more  borax.  Melt  with  low  red  heat.  Stir 
with  the  heated  end  of  a  piece  of  nail-rod  as  long  as  that 
melts  away  rapidly;  then,  from  the  same  end  of  the  rod, 
cut  a  piece  of  a  length  to  suit  the  pot  and  put  the  piece 
into  the  pot,  together  with  any  lead  or  slag  that  may  have 
adhered  to  it.  Cover  and  heat  to  rather  bright  redness  for 
ten  minutes.  Remove  the  remnant  of  iron,  after  wash- 
ing it  in  the  slag  (see  Part  I,  page  61);  shake  and  tap  as 
in  the  assay  of  gold  and  silver  ores,  and  either  pour  into 
the  assay  mould,  or,  which  is  better  in  the  case  of  poor 
ores,  cool  and  break  the  pot. 

If  the  button  is  coppery,  not  enough  sulphur  was 
present;  if  hard  or  brittle,  the  assay  probably  required 
a  longer  time  in  the  furnace,  or  it  contains  antimony, 
in  which  case  it  will  be  better  to  repeat  the  assay,  using 
more  soda  and  omitting  the  iron  and  flour,  also  the  sul- 
phur if  the  ore  is  antimonial  galena,  but  if  the  ore  is  a 
thoroughly  oxidized  one  the  sulphur  may  be  increased. 
Clean  it  by  hammering  and  brushing.  Jf  the  ore  con- 
tained arsenic,  the  button  will  consist  of  two  distinct 
parts,  the  one  hard  and  brittle,  which  is  iron  arsenide, 
to  be  rejected,  the  other  malleable,  which  is  lead.  They 
can  be  separated  readily.* 

If  100  grains  of  ore  were  taken  for  the   assay,  the 

*See  also  Appendix  to  Part  I. 


LEAD   ORES.  .  91 

weight  of  the  button  in  grains  is  the  percentage;  if  10 
grammes,  the  button  weight  in  grammes  multiplied  by 
10.  An  addition  of  5  per  cent,  of  the  button  weight 
may  be  allowed  for  loss. 

Carbonate  ores,  free  from  copper  and  zinc,  require  only 
to  be  melted  with  soda,  borax  and  flour,  but  it  is  as  well 
to  add  a  nail  or  piece  of  thick  wire,  in  case  there  may  be 
some  sulphate  or  arsenate  also.  (A  mixture  of  carbonate 
and  sulphate,  in  the  right  proportions  will  yield  all  the 
lead  without  iron  or  carbon,  but  this  cannot  be  depended 
on  when  the  proportions  are  unknown,  and  arsenic  in 
any  form  calls  for  iron.)  The  button  may  be  cupelled 
for  precious  metal,  and,  if  worth  notice,  the  weight  of 
that  found  deducted. 

Wet  Assay. — This  is  more  accurate  than  any  fire 
assay  for  lead. 

Treat  a  suitable  quantity  of  the  very  finely  powdered 
ore  with  strong  nitric  acid  in  a  porcelain  dish,  using  as 
a  cover  an  inverted  funnel  of  such  a  size  as  to  rest  within 
the  rim  of  the  dish;  or  in  a  casserole  covered  with  a 
clock-glass,  concave  side  upward.  Boil  gently  on  the 
sand-bath  or  coal-oil  stove  until  the  residue  is  as  nearly 
white  as  it  can  be  made,  and  the  most  of  the  acid  has 
evaporated.  Cool,  and  dilute  with  water.  Add  dilute 
sulphuric  acid  as  long  as  it  makes  a  precipitate;  not 
much  more,  as  a  large  quantity  may  throw  down  a  p.  p. 
of  lime  where  only  lead  is  wanted.  Remove  the  cover, 
and  wash  into  the  dish  any  matter  that  may  be  on  it. 
Filter,  and  wash  with  water  slightly  soured  with  sul- 
phuric acid,  until  the  drippings  no  longer  produce  more 
than  a  faint  white^  cloud  in  a  little  solution  of  sodium 
carbonate. 


92  ASSAYING 

Pierce  the  filter  with  a  glass  rod,  and  wash  the  p.  p 
off  it  into  a  porcelain  dish;  then  carefully  remove  the  filter 
from  the  funnel,  unfold  it,  and  wash  into  the  dish  any 
portion  of  p.  p.  which  may  have  lodged  in  the  folds. 
Use  no  more  water  than  is  necessary,  and  if,  neverthe- 
less, the  quantity  is  large,  let  the  p.  p.  settle,  and  pour  off 
a  part  of  the  water.  Add  as  much  sodium  carbonate  as 
will  dissolve,  and  boil  gently  for  half  an  hour,  keeping 
the  vessel  covered,  as  before,  by  an  inverted  funnel  or  a 
glass.  Add  a  little  more  sodium  carbonate,  and  observe 
if  it  causes  effervescence.  It  will  not  if  enough  has  been 
used.*  Filter,  and  wash  with  water  until  the  drippings 
no  longer  make  a  precipitate  in  solution  of  barium  chlo- 
ride, nor  in  one  of  copper  sulphate.  The  lead  is  now  on 
the  filter  in  the  form  of  carbonate. 

Place  a  clean  beaker  under  the  filter;  again  pierce  that, 
and  wash  it  clean.  Redissolve  the  lead  carbonate  by 
dilute  nitric  acid,  or  by  acetic  acid-f.  Add  dilute  sul- 
phuric acid  freely.  Allow  the  p.  p.  to  settle ;  filter ;  wash 
with  water  soured  with  sulphuric  acid,  and  lastly,  once 
with  pure  water.  The  lead  is  now  again  on  the  filter  in 
the  form  of  sulphate,  as  it  was  after  the  first  filtration, 
but  freed  from  impurity. 

Dry  the  p.  p.  on  the  filter ;  transfer  it  to  a  small  porce- 
lain basin;  heat  nearly  to  redness;  cool  and  weigh.  If 
very  particular,  burn  the  filter  in  another  basin  until  the 

•Sodium  bicarbonate  may  be  used  in  the  first  place,  but  will  not 
answer  for  this  test.  The  potassium  salts  may  be  used  in  place  of  the 
corresponding  sodium  salts. 

+The  lead  carbonate  may  be  dissolved  on  the  filter  without  previous 
removal. 


\  LEAD   ORES.  93 

ashes  are  white;  moisten  with  nitric  acid;  add  a  drop  of 
sulphuric  acid;  dry,  and  add  to  the  lead  sulphate  in  the 
first  basin  before  heating.  To  be  still  more  exact,  burn 
another  filter  of  the  same  size,  treat  the  ashes  in  the  same 
way,  and  put  them  on  the  weight  pan  when  weighing. 
The  weight  of  the  lead  sulphate  multiplied  by  0.6833 
gives  the  weight  of  the  lead. 

Instead  of  heating  and  weighing  the  p.  p.,  it  may  be 
mixed  with  about  twice  its  weight  of  potassium  cyanide, 
placed  in  a  small  crucible,  covered  with  salt,  melted  at  as 
low  heat  as  possible,  cooled,  extracted  by  breaking  the 
pot,  and  weighed  as  pure  lead. 

Again,  and  better  if  the  ore  contain  much  lime,  acetic 
acid  being  used  for  the  dissolving  of  the  lead  carbonate, 
the  lead  may  be  precipitated  as  chromate  by  solution  of 
potassium  bichromate,  collected  on  a  filter,  dried  on  a 
water-bath,  and  wei|fhed,  filter  and  all,  another  filter  of 
the  same  weight  being  dried  at  the  same  time  and  placed  on 
the  weight  pan  of  the  scales.  Calculate  68.94  per  cent, 
of  the  weight  as  lead. 

Time  may  be  saved  by  proceeding  as  follows :  Instead  of 
boiHng  the  first  residue  with  sodium  carbonate,  digest  it, 
cold,  with  a  mixture  of  ammonia  and  acetic  acid  in 
which  the  acid  is  in  slight  excess,  or  with  solution  of 
ammonium  acetate  to  which  a  little  acetic  acid  has  been 
added.  Filter  and  wash.  To  the  filtrate,  including  the 
washings,  add  diluted  sulphuric  acid  as  long  as  it  causes 
a  p.  p.  Again  filter;  wash  with  soured  water;  dry,  cal- 
cine and  weigh.  The  lead  is  in  the  form  of  sulphate,  as 
in  the  first  process. 

Unless  for  particular  work,  the  lead  sulphate  may  be 


94  ASSAYING 

weighed  on  the  filter  after  drying  at  248°  Fahrenheit,  a 
similar  filter,  similarly  dried  being  placed  on  the  weight 
pan. 

Lime  is  the  chief  common  constituent  of  lead  ores 
which  is  likely  to  cause  an  erroneous  result.  If  calcium 
sulphate  (sulphate  of  lime)  is  allowed  to  remain  with  the 
lead  sulphate  at  the  first  filtration,  it  will  also  be  con- 
verted into  carbonate  by  the  boiling  with  sodium  carbon- 
ate, or  it,  as  well  as  the  lead  sulphate,  will  be  dissolved 
by  ammonium  acetate.  In  either  case  it  is  liable  to  be 
thrown  down  again,  together  with  the  lead,  as  sul- 
phate in  the  last  precipitation.  But,  while  lead  sulphate 
is  very  little  soluble  in  water,  especially  if  the  water  con- 
tains sulphuric  acid,  calcium  sulphate  is  considerably  so. 
It  is  for  the^e  reasons  that  stress  is  laid  on  the  use  of 
quite  dilute  acid  for  the  precipitation,  and  of  acid  water 
for  the  washing.  It  has  already  been  shown  that  the 
lead  may  be  precipitated  from  the  acetic  acid  solution  as 
chromate,  any  lime  present  then  remaining  in  solution 
and  passing  ofi*  in  the  filtrate.  I  also  find  that  an  acid 
solution  of  ammonium  acetate  saturated  with  lead  sul- 
phate can  still  dissolve  calcium  sulphate  freely;  hence 
the  latter  may  be  removed  from  the  former  by  washing 
with  such  a  saturated  solution,  after  which  that  must  be 
washed  out  by  water. 


COPPER    ORES.  95 


COPPER  ORES. 


The  fire  assay  of  copper  is  not  very  satisfactory,  es- 
pecially in  unpracticed  hands;  it  may,  however,  answer 
the  purpose  of  a  prospector.  The  ore  must  be  ground  to 
pass  a  40-mesh  sieve.  Poor  ores,  and  all  which  contain 
lime  or  baryta  and  sulphur  in  any  form,  should  be  sub- 
mitted to  a  matte  smelting ;  the  first  in  order  to  obtain 
an  enriched  product  on  which  to  operate;  the  second  in 
order  to  remove  calcium  or  barium  sulphate  which  would 
cause  a  loss  of  copper.  It  is  well  to  add  a  large  nail  to 
a  matte  smelting  to  separate  any  lead  which  may  be 
present. 
ORES   CONTAINING    LESS    THAN    8    PER   CENT.    OF    COPPER. 

Ore 400  grains. 

Borax  glass 400      " 

Flour 20 

Sulphur 10 

Mix  by  grinding  in  wedgewood  mortar;  put  in  pot, 
cover  with  salt,  and  over  that  put  400  grains  more  borax 
glass.  The  sulphur  and  flour  may  be  omitted  if  the  oi'e 
contains  sulphurets,  zinc-blende  excepted,  provided  none 
of  the  higher  metal-oxides  are  present.  If  there  is 
any  suspicion  of  lead,  add  a  nail.  Melt  slowly  and  finish 
with  strong  heat.  Remove  the  nail ;  cool  and  break  the 
pot.  Separate  the  matte  from  the  overlying  slag  and 
from  lead,  if  any,  and  reserve  for  further  treatment. 


96  assaying 

Richer  Ores  with  Lime  or  Baryta  Gangue  and  Con- 
taining Sulphur  Either  as  Sulphurets  of  Any 
Kind,  or  Combined  with  the  Gangue  as  Gypsum 
OR  HeavySpar.* 

Ore 100  grains. 

Borax  glass 100      " 

Sulphur  if  required. 
Mix,  put  in  pot,  cover  with  salt  and  more  borax,  and  add 
a  nail  if  lead  is  suspected.     Melt,  etc.,  as  before.     Re- 
serve the  matte. 

Rich  Sulphuretted  Ores  Without  Lead,  Lime,  or 
Baryta. — These  include  the  mattes  from  the  preceding 
as  well  as  natural  ores.  Pulverize;  roast  in  a  roasting 
dish  in  the  muffle,  beginning  with  a  low  heat,  and  rais- 
ing it  gradually  to  bright  redness,  stirring  the  ore  at 
intervals  with  a  piece  of  wire.  If  the  ore  is  inclined  to 
decrepitate  and  fly  out  of  the  dish,  it  must  be  covered 
by  another  roasting  dish  inverted  and  having  some 
notches  in  the  edge  and  a  hole  in  the  middle,  and  must 
be  cooled  before  being  uncovered  for  the  stirring.  It. will 
soon  cease  decrepitating.  When  no  more  odor  is  per- 
ceptible from  the  red-hob  ore,  cool,  grind  again  with  the 
addition  of  one-tenth  part  of  coke.  Roast  again,  ob- 
serving whether  arsenic  is  present  or  not.  Arsenic  is 
known  by  an  odor  like  that  of  garlic.  Roast  until  all 
the  coke  is  burned  to  ashes.  If  arsenic  was  observed, 
repeat  the  grinding  with  coke  and  roasting  until  it  is  all 
expelled.  At  last  place  on  the  ore  a  piece  of  ammonium 
carbonate  of  10  or  20  grains  weight,  cover  and  heat  until 
the  carbonate  has  evaporated;  ,this  removes  any  lingering 
sulphur.     The  ore  is  now  in  the  following  class. 

*  In  this  and  preceding,  strontia  may  be  regarded  in  the  same  light 
as  baryta. 


COPPER   ORES.  97 

Rich  Oxidized  Ores.: — If  the  ore  is  a  natural  oxide, 


the  assay  must  be  weighed  and  calcined  by  heating  to 
redness  in  a  roasting  dish.     Add  to  the  assay — 

Soda an  equal  weight. 

Argol 

Lime  .  . .  >  » .  .one-fourth  the  weight. 
And,  if  it  contains  much  quartz,  a  little  powdered  iron- 
stone (hematite)  or  forge  scale.  Mix  well  in  the  wedge- 
wood  mortar.  Place  in  a  pot  which  should  not  be  more 
than  two-thirds  filled.  Cover  with  a  mixture  of  soda 
and  argol  in  equal  parts,  and  on  that  a  weight  of  borax 
glass  equal  to  the  weight  of  the  assay.  Heat  very 
slowly  to  dull  redness  for  fifteen  minutes,  then  fuse  thor- 
oughly with  high  heat,  and  remove  from  the  fire  without 
delay.  Wash  the  side  of  the  pot  by  the  slag  as  in  an 
assay  for  gold  and  silver,  tap  to  settle  all  globules,  allow 
to  cool,  and  break  the  pot. 

The  copper  should  be  found  at  the  bottom  of  the  pot 
in  a  single  button.  If  the  button  is  tolerably  malleable,  - 
and  when  broken  or  cracked  is  found  to  be  of  a  good 
red  color  all  through,  it  is  pure  enough,  and  may  be 
weighed.  If  it  is  black,  gray,  or  mottled,  it  must  be 
refined  by  cupellation.  The  slag  should  be  neither  red 
nor  green.  The  side  of  the  pot  should  be  but  little  col- 
ored with  red  or  green. 

Refining  the  Impure  Copper. — Place  the  button  on 
a  highly  heated  cupel,  and  an  equal  weight  of  pure  cop- 
per on  another.  Add  to  each  one- tenth  part  of  lead, 
and  close  the  muffle  after  placing  some  glowing  coals  in 
it.     When  the  buttons  are  well  melted,  open  the  muffle 


98  ASSAYING 

to  allow  of  the  entrance  of  air ;  the  refining  then  begins. 
The  button  behaves  much  in  the  same  manner  as  one  of 
silver,  when  nearly  free  from  lead,  but  the  final  bright- 
ening is  less  vivid.  The  heat  must  be  higher  than  for 
silver,  and  should  be  such  as  that  the  copper  solidifies  at 
the  instant  when  the  lead  leaves  it.  The  button  should 
then  appear  greenish.  If  it  does  not  seem  to  be  pure, 
add  another  tenth  of  lead,  both  to  the  assay  and  to  the 
pure  copper  beside  it.  Continue  thus  adding  lead  by 
tenths  and  cupelling  it  off,  until  the  assay  button  is 
pure.  Remove  from  the  muffle  and  plunge  both  of  the 
buttons  into  cold  water  as  soon  as  possible  after  solidi- 
fication in  order  to  stop  oxidation.*  Clean  by  hammer- 
ing and  brushing ;  weigh,  and  to  the  assay  button  weight 
add  as  much  as  the  pure  copper  has  lost.  If  pure  copper 
is  not  at  hand,  refine  the  assay  button  and  weigh  it; 
then  cupel  it  again  with  as- many  tenths  of  lead  as  were 
used  in  the  refininof  •  weisrh  ao^ain,  and  to  the  first  weight 
add  as  much  as  has  been  lost  in  the  second  cupellation. 
The  percentage  must  be  calculated  on  the  quantity  of 
ore  originally  taken,  whether  matte  smelted  or  not. 

Argol  is  crude  cream  of  tartar;  an  intimate  mixture 
of  one  part  of  flour  and  four  of  soda  may  be  used  in- 
stead. 

Wet  Assay. — Unless  with  very  pure  oxidized  ores, 
"the  wet  method  is  less  troublesome,  as  well  as  more  exact 
than  a  fire  assay.  A  suitable  quantity  of  the  finely 
powdered  ore  is  gently  boiled  with  a  mixture  of  nitric 
and  hydrochloric  acid,  more  of  the  first  than  of  the  last, 

*Some  operators  cover  the  button  with  charcoal  powder  at  the  in- 
stant of  brightening,  with  the  same  view. 


COPPER    ORES.  99 

until  decomposed,  the  sulphur,  if  any  be  prasent,  either 
being  completely  oxidized  into  sulphuric  acid,  or  melted 
to  clear  amber  colored  drops. 

It  is  best  that  the  sulphur  be  oxidized.  The  oxidation 
is  promoted  by  adding,  from  time  to  time,  a  few  crystals 
of  potassium  chlorate.  As  the  solution  is  to  be  evapo- 
rated, it  is  best  made  in  a  casserole  covered  by  a  clock- 
glass,  or  in  a  dish  covered  by  a  funnel  which  fits  inside 
of  the  dish.  It  may  be  made  in  a  mattrass,  which  is 
very  suitable  for  the  boiling,  but  then  it  must  be  trans- 
ferred to  a  dish  or  other  open  vessel  for  the  evaporation, 
or  time  must  be  lost.  If  the  sulphur  is  not  dissolved  by 
oxidation,  the  assay  must  be  cooled  until  the  drops  of 
sulphur  become  solid  so  that  they  may  be  removed  to  a 
small  dish  and  burned.  Any  residue  is  then  to  be  dis- 
solved in  hydrochloric  acid  and  added  to  the  main  solu- 
tion. 

The  solution  must  now  be  evaporated  to  dryness  after 
the  addition  of  sulphuric  acid  to  insure  the  expulsion  of 
all  nitric  acid.  Dry  with  gentle  heat,  not  causing  the 
liquid  to  bubble  and  spirt;  toward  the  last  it  may  be 
necessary  to  stir  the  thickening  mass  in  order  to  prevent 
spirting.  Allow  to  cool ;  add  a  little  water  and  a  few 
drops  of  hydrochloric  or  sulphuric  acid.  Allow  to  re- 
main half  an  hour  in  a  warm  place,  and  stir  once  or 
twice  with  a  glass  rod.  Filter  and  wash,  receiving  the 
liquid  in  a  clean  beaker.  To  the  filtrate  and  washings 
in  the  beaker  add  ammonia  in  excess,  that  is  until  the 
liquid  smells  strongly  of  it. 

If  a  considerable  brown  flocculent  p.  p.  forms  on  the 
addition  of  ammonia,  any  arsenic  which  may  be  present 


100  ASSAYING 

will  go  with  that;  otherwise  add  "magnesia  mixture" 
as  long  as  it  produces  a  turbidity.  Let  the  assay  stand 
as  long  as  is  convenient,  in  a  warm  place,  then  filter  and 
wash  with  water  containing  ammonia  as  long  as  the 
drippings  have  a  blue  tint.  To  the  filtrate  add  hydro- 
chloric or  sulphuric  acid  until  it  is  quite  acid;  warm 
slightly,  and  place  in  the  beaker  a  piece  of  clean  sheet 
iron  of  such  a  size  that,  while  completely  covered  by  the 
liquid,  it  does  not  lie  flat  on  the  bottom  of  the  vessel. 

Heat  the  liquid  gradually  to  almost  boiling.  Bubbles 
of  hydrogen  gas  will  be  seen  rising  from  the  surface  of 
the  iron,  and  this  action  must  be  kept  up,  in  moderation, 
by  adding  hydrochloric  or  sulphuric  acid  from  time  to 
time.  When  the  liquid  is  quite  colorless,  test  it  by  hold- 
ing a  clean  wire  or  other  piece  of  iron  in  it  for  half  a 
minute ;  if  the  wire  is  not  discolored  no  copper  remains 
in  the  solution.  A  piece  of  zinc  is  even  better  than  iron 
for  the  test,  and  zinc  may  be  used  in  place  of  iron  for 
the  precipitation  of  the  copper  if  it  is  certain  that  no 
nitric  acid  nor  nitrates  remained  after  the  evaporation 
with  sulphuric  acid.  The  beaker  should  be  covered  dur- 
ing the  precipitation  of  the  copper,  to 'exclude  dust. 

The  copper  is  now  in  the  metallic  state,  precipitated 
by  the  iron  a  corresponding  portion  of  which  has  been 
dissolved.  Pour  off  a  great  part  of  the  liquid,  with  care 
that  no  copper  goes  with  it.  Transfer  the  remaining 
contents  of  the  beaker  to  a  dish*,  and  detach  the  copper 
from  the  iron  by  means  of   a  clipped  feather.     Reject 

*This  is  best  done  by  filling  the  beaker  with  water,  inverting  the 
dish  over  it,  and  operating  in  a  manner  similar  to  that  described  for 
cupping  a  gold  assay,  but  the  beaker  must  be  removed  by  sliding  it 
quickly  to  one  side. 


COPPER  ORES.  101 

the  iron  and  wash  the  copper  six  times  with  hot  pure 
water,  draining  it  off  as  closely  as  possible  each  time  into 
another  dish  in  which  any  small  particles  of  copper  that 
may  unavoidably  escape  may  be  settled  and  eventually 
recovered.  The  last  two  washings  are  best  made  with 
alcohol,  but  it  is  not  essential.  The  spongy  copper  may 
be  compacted  by  pressing  with  the  finger,  or  the  bottom 
of  a  test-tube,  to  aid  the  washing  and  draining.  Some 
light  black  particles  of  carbon  from  the  iron  will  prob- 
ably be  seen;  these  should  be  washed  away  as  much  as 
possible.  A  slight  discoloration  of  the  precipitated  cop- 
per may  often  be  removed  by  gentle  boiling  in  dilute 
hydrochloric  acid.    The  proper  color  is  a  pure  copper  red. 

The  washed  and  drained  metal  is  to  be  dried  in  the 
dish  on  the  water-bath.  The  percentage  is  calculated 
for  the  weight  of  ore  used,  which  may  vary,  with  the 
supposed  richness  and  the  delicacy  of  the  balance,  from 
20  grains  to  several  hundred. 

Russia  sheet  iron  is  suitable  for  the  precipitation  of 
copper  if  the  scale  is  removed  by  means  of  warm  dilute 
hydrochloric  or  sulphuric  acid  and  rubbing.  Good  wire 
cut  to  a  suitable  length  is  also  proper;  it  may  be  cleaned 
with  sand-paper.  If  zinc  is  used,  it  should  be  such  as 
dissolves  without  residue  in  dilute  hydrochloric  acid. 

Magnesia  mixture,  for  the  removal  of  arsenic  in  the 
case  of  an  ore  containing  little  or  no  iron,  is  prepared 
by  dissolving  epsom  salts  in  water  and  adding,  first  sal 
ammoniac  (ammonium  chloride),  and  then  ammonia. 
The  ammonia  should  produce  no  p.  p.,  and  it  will  not  if 
enough  sal  ammoniac  be  present. 

The  dried  copper  should  retain  a  good  color,  and  should 


102  ASSAYING 

not  adhere  to  the  dish  in  which  it  was  dried,  and  it  will 
not  if  well  washed.  The  result  is  more  reliable  if  the 
dried  copper  is  calcined  at  a  red  heat  in  the  muffle,  cooled, 
moistened  with  nitric  acid,  again  heated  to  redness,  cooled 
and  weighed.  It  is  then  in  the  form  of  black  oxide,  of 
which  79.85  per  cent,  is  copper. 

An  oxidized  ore,  whether  a  natural  product  or  the  re- 
sult of  roasting  a  sulphuret,  if  free  from  arsenic,  anti- 
mony, and  bismuth,  requires  only  to  be  decomposed  by 
hydrochloric  and  sulphuric  acid,  the  solution  filtered, 
and  the  copper  precipitated  by  iron  or  zinc,  etc.  The 
red  oxide,  however,  requires  an  addition  of  potassium 
chlorate  to  the  solution  in  quantity  sufficient  to  convert 
that  from  a  brown  and  muddy  appearance  to  a  clear 
green,  after  which  it  must  be  boiled  for  some  time  to 
expel  excess  of  chlorine  before  the  precipitation  is  at- 
tempted. Nitric  acid  will  answer  as  well  as  potassium 
chlorate,  only  then  the  solution  must  be  evaporated  to 
dryness  as  in  the  first  described  process.  Ores  which 
do  not  yield  all  their  copper  to  acids  may  be  made  to 
do  so  by  previous  fusion  with  soda  in  a  poicelain  crucible. 

A  better  way  in  which  to  precipitate  the  copper  is  to 
pour  the  solution  into  a  platinum  dish  of  known  weight, 
and  add  a  piece  of  pure  zinc.  The  copper  is  precipitated 
on  the  dish,  to  which  it  adheres,  making  the  washing  easy. 
The  whole  of  the  zinc  is  to  be  dissolved,  acid  being  added, 
if  necessary,  for  that  purpose  until  no  more  bubbles  are 
seen.  The  copper  is  dried  and  weighed  still  on  the  dish, 
the  known  weight  of  the  latter  deducted,  leaving  the 
net  weight  of  the  copper.  The  copper  is  removed  from 
the  dish  by  nitric  acid,  which  does  not  attack  the  dish. 


COPPER   ORES.  103 

But  little  inferior  is  the  method  of  precipitating  the 
copper  in  a  porcelain  or  glass  vessel  in  which  is  placed 
a  weighed  piece  of  platinum  foil,  and,  in  contact  with 
that,  a  piece  of  zinc.  The  copper  is  precipitated  on  the 
platinum.  In  these  processes,  all  nitric  and  hydrochloric 
acid  is  expelled  from  the  solution  by  boiling  down  with 
sulphuric  acid. 

The  method  which  is  generally  considered  the  best  at 
present  is  the  precipitation  by  electrolysis,  in  which  a 
current  of  electricity  is  passed  through  the  solution  by 
means  of  platinum  electrodes,  on  one  of  which  the  cop- 
per is  deposited  in  a  compact  form.  The  nitric  solution 
is  used  in  this  process,  hydrochloric  acid  being  injurious. 
The  method  requires  special  apparatus  and  experience, 
and  though  very  exact  is  equaled  in  this  respect  and 
surpassed  in  point  of  expedition  by  my  new  process,  to 
be  described  shortly. 


104  VOLUMETRIC   ASSAYS 


VOLUMETRIC  ASSAYS  OF  COPPER. 


There  are  a  great  naany  methods  of  estimating  copper 
volumetrically,  that  is,  by  the  volume  of  a  reagent 
which  is  found  to  be  necessary  to  produce  or  complete  a 
certain  effect  in  the  suitably  prepared  solution.  The  one 
most  commonly  used  depends  on  the  fact  that  the  blue 
ammoniacal  solution  of  copper  is  decolored  by  a  solution 
of  potassium  cyanide.     This  is  generally  known  as 

Parkes'  Process. — Take  10  grains,  or  1  gramme,  of 
pure  copper:  dissolve  it  in  nitric  acid;  add  ammonia  un- 
til the  p.  p.  at  first  formed  is  redissolved  to  a  blue  liquid; 
add  water  to  make  about  one-third  of  a  pint  (in  a 
beaker).  Charge  a  Mohr  burette  with  a  solution  of  po- 
tassium cyanide  made  by  dissolving  one  troy  ounce  in 
^ve  and  a  half  fluid  ounces  of  water  (or  the  water  may  be 
weighed)  and  filtering  if  necessary.  Run  the  liquid  from 
the  burette,  into  the  blue  solution  of  copper,  stirring  that 
with  a  glass  rod,  until  the  blue  color  becomes  faint  and 
purplish;  continue  cautiously,  adding  the  cyanide  little 
by  little,  finally  drop  by  drop  with  intervals  between, 
until  only  a  faint  tint  remains  which  disappears  in  a  few- 
minutes,  leaving  the  liquid  colorless.  Observe  how  many 
c.  c.  of  the  cyanide  have  been  used,  by  the  marks  on  the 
burette,  and  note  the  number.  The  cyanide  solution  is 
thus  titrated,  that  is,  it  is  known  what  volume  of  it  cor- 
responds to  10  grains  or  to  1  gramme  of  coppei-  in  the 


OF    COPPER.  105 

solution.  The  titrated  cyanide  solution  should  be  kept 
in  a  dark-colored  stoppered  bottle. 

To  assay  an  ore :  take  20  grains  or  2  grammes,  more  or 
less  according  to  the  grade  of  richness,  and  make  an 
acid  solution  by  one  of  the  methods  previously  described, 
or  by  nitric  acid  alone.  Add  ammonia  in  considerable 
excess,  and  heat  moderately  for  some  time.  If  there  is 
any  considerable  quantity  of  insoluble  matter,  filter,  and 
wash  with  water  containing  ammonia  until  that  passes 
through  colorless.  The  entire  volume  of  solution,  includ- 
ing the  washings  if  filtered,  should  be  about  one-third 
of  a  pint.  When  quite  cold  add  solution  of  potassium 
cyanide  from  the  burette  precisely  as  in  titrating,  noting 
the  quantity  used. 

The  determination  of  the  assay  is  now  a  mere  sum  in 
proportion  or  the  "rule  of  three."  For  instance,  if  10 
grains  of  pure  copper  required  4-5  c.  c.  of  cyanide  solu- 
tion, and  the  ore  assay  required  63.5  c.  c.  then  45:10:  : 
63.5  :  the  copper  in  the  assays  14.1  grains,  and  if  20 
grains  of  ore  were  taken,  the  percentage  is  14.1x5=70.5 
or,  if  50  grains  of  ore  were  used,  14.1x2  =  28.2  per  cent. 

The  presence  of  manganese  interferes  a  little  with  the 
decoloration.  This  is  obviated  by  an  addition  of  am. 
monium  carbonate.  Arsenic  also  interferes  but  may 
be  prevented  by  "  magnesia  mixture,"  added  before  filter- 
ing. Nickel,  cobalt,  or  zinc  is  fatal  to  the  accuracy  of 
the  process.  When  either  of  these  is  present,  the  copper 
should  be  precipitated  by  iron  or  zinc  as  in  the  first  de- 
scribed process,  washed,  and,  without  drying,  dissolved  in 
nitric  acid,  blued  by  ammonia  and  determined  as  above. 

The  process  is  rapid  and  easy,  therefore  popular,  but 
not  always  accurate.     The  quantity  of  ammonia  and  of 


106  VOLUMETRIC   ASSAYS 

the  different  acids  used,  affects  the  result.  On  account 
of  variations  of  temperature,  a  check  test  on  pure  copper 
should  be  made  with  each  set  of  assays  unless  the  tem- 
perature is  nearly  constant.  This  applies  however  to  all 
volumetric  processes.  The  cyanide  solution  is  liable  to 
change,  despite  the  precaution  of  keeping  it  as  much  as 
possible  in  darkness,  hence  too  large  a  quantity  should 
not  be  made  at  one  time ;  the  directions  given  above  for 
making  it  only  indicate  approximately  the  proportions  to 
be  used,  which  may  be  modified  to  suit  convenience,  and 
the  quantity  prepared  may  be  adapted  to  the  expected 
demand. 

*=nx^  The  cuts  show  two  kinds  of  burettes  which 

are  suitable  for  this  and  other  volumetric 
assays.  The  Mohr  burette  is  the  most  conven- 
ient. It  may  be  of  50  or  100  c.  c.  capacity; 
should  be  graduated  to  one-tenth  c.  c.  and  fur- 
nished with  Erd man's  float.  The  discharge  by 
means  of  rubber  tube  and  pinch-cock  is  prefer- 
able, for  common  use,  to  that  by  a  glass  cock. 


1 


"^-' ' [ ' " ~" 


mohr's  burettes, 

^BurettT"  WITH   PINCH   COCK,   RUBBER    TUBING    AND    TOP. 

Size 10x1-10    10x1-5    25x1-10    25x1-5    50x1-10    50x1-5 

Price..-.      $1.25         1.12  1.40         1.25  1.60  1.50 

Bize 100x1-5    100x1-1    200x1-1 

Price S2.00         1.50  2.00 


OF   COPPER.  107 

Assay  by  Amalgamation. — This  may  answer  the 
purpose  where  means  are  wanting  for  the  other  methods. 
Take  100  grains  or  more  of  the  powdered  ore,  and,  if  it 
contains  sulphurets,  roast  it.  Grind  it  in  an  iron  mortar, 
warmed,  with  water  enough  to  make  a  pulp,  and  such  a 
quantity  of  a  mixture  of  iron  sulphate  (copperas  or  green 
vitriol)  and  salt  as  may  be  necessary  to  cause  a  copper 
stain  on  a  piece  of  clean  iron  held  in  the  hot  pulp  for  a 
few  seconds;  also  a  little  mercury.  Continue  rubbing 
and  stirring  with  the  pestle  until  the  latter  no  longer 
takes  up  mercury  when  lifted  out,  and  a  bright  piece  of 
iron  is  not  stained  by  the  pulp.  Then  wash  the  pulp 
away  by  a  stream  of  water,  leaving  the  mercury.  Strain 
the  mercury  through  a  piece  of  wet  buckskin  by  twist- 
ing. Copper,  perhaps  also  lead,  gold,  and  silver,  will 
remain  in  the  form  of  a  ball  of  amalgam.  Tie  the  ball 
in  a  small  piece  of  cotton  cloth,  as  a  dumpling  is  tied; 
put  it  into  a  crucible;  cover  it  with  powdered  charcoal; 
heat  it  gradually  to  redness ;  then  add  some  borax  and  a 
piece  of  charcoal  and  heat  strongly.  When  cold,  break 
the  pot  in  which  a  button  of  metal  will  be  found.  If 
the  button  is  good  copper,  weigh  it;  if  not,  refine  it  as 
directed  for  the  crucible  assay,  and  then  weigh.  If  the 
button  remains  of  a  pale  color  after  refining,  it  probably 
contains  a  large  proportion  of  silver.  Treat  it  by  scori- 
fication  and  cupellation  for  precious  metal.  From  the 
net  weight  of  copper  obtained,  calculate  the  percentage 
for  the  weight  of  ore  taken. 

New  Process. — This  is  the  writer's  own  invention. 
It  is  not  difficult  and,  in  point  of  accuracy,  is  believed  to 
be  inferior  to  none.     Copper  in  ammoniacal  solution  is 


108  VOLUMETRIC   ASSAYS 

completely  precipitated  by  solution  of  potassium  zanthate. 
By  this  reagent  copper  is  easily  detected  in  a  solution 
which  is  not  visibly  blued  by  addition  of  ammonia. 
Neither  arsenic,  nickel,  zinc,  manganese,  nor  the  earths 
interfere.  So  delicate  is  this  method  that  it  is  possible 
to  make  the  assay  on  one  decigramme  of  ore  to  one- 
tenth  of  one  per  cent.  I  prefer  to  operate  on  larger  quan- 
tities when  accuracy  is  requisite. 

Weigh  ten  grains,  or  one-half  gramme,  of  pure  copper, 
and  dissolve  it  in  nitric  acid.     Add  ammonia  in  excess, 
and  water  to  make  about  half  a  pint  of  soluticm,  in  a 
beaker  of  thin  clear  glass.     From  a  Mohr  burette,  which 
should  be  graduated  at  least  to  one-fifth  c.  c.  run  in  solu- 
tion of  potassium  zanthate,  stirring  gently  the  while,  or 
at  short  intervals,  with  a  glass  rod.     The  solution  in  the 
beaker  soon  appears  green  from  admixture  with  the  yel- 
low p.  p.     As  long  as  a  green  color  is  plainly  seen  on 
stopping  the  flow  of  the  zanthate,  and  gentle  stirring, 
more  zanthate  may  be  freely  added.     When  the  green 
color  grows  faint,  proceed  with  caution.     Stir  actively 
for  half  a  minute  or  more,  but  avoid  making  froth.     Al- 
low the  p.  p.  to  settle  to  some  extent,  and  if  the  liquid  is 
not  clear  enough,  stir  again,  but  as  long  as  a  green  tint 
is  perceptible  it  is  not  necessary  that  it  should  be  very 
clear.     Continue  adding  zanthate,  by  quarter  c.  c.  or  1<  s^, 
stirring  and  settling.     When  near  the  en<l,  stir  an  i  settle 
until  the  liquid  is  no  longer  turbid,  although  flecks  of  the 
p.  p.  may  remain   suspended.     Alter  this   a  very  little 
stirring  will  suffice  after  each  addition  of  a  dr-op  or  two 
of  zanthate.     When  an  addition  of  zanthate  causes  no 
cloud  in  the  liquid,  the  precipitation  is  complete  and  a 
slight  excess  of  the  zanthate  is  present. 


OF   COPPER.  109 

For  the  purpose  of  verification,  a  second  assay  may  be 
made,  and  nearly  the  quantity  of  zanthate  required  run 
in  at  once,  finishing  with  caution  as  before.  To  verify 
the  presence  of  a  slight  excess  of  zanthate,  stir  and  settle; 
then  draw  through  the  clear  liquid  the  end  of  a  small 
glass  rod  moistened  with  an  ammoniacal  solution  of 
copper.  Either  a  faint  cloud  will  appear  near  the  sur- 
face, or  minute  drops  of  the  blue  solution  will  sink 
through  the  liquid,  leaving  thin  white  streaks  behind 
them.  The  appearance  of  these  streaks,  which  assume 
the  form  of  wreaths  from  the  motion  of  the  liquid,  is 
very  beautiful. 

Toward  the  end  of  the  operation,  a  record  should  be 
kept  of  the  quarter  or  tenth  c.  c.  of  zanthate  added,  in 
order  that,  in  finally  reading  the  burette,  the  last  addi- 
tion, which  produced  no  p.  p.  and  was  therefore  not  re- 
quirv^d,  and  half  of  the  one  before  the  last,  because  it  was 
probably  only  partially  requisite,  may  be  rejected.  Thus 
it  is  known  how  many  c.  c.  of  the  zanthate  are  required 
to  precipitate  the  quantity  of  copper  taken,  wiiich  con- 
stitutes the  titre  of  the  solution  (or  the  standard). 

To  assay  an  ore,  take  such  a  weight  as  may  be  supposed 
to  contain  from  one  to  ten  grains  of  copper,  or  a  correspond- 
ing proportion  in  grammes  if  that  system  of  weight  is  in 
use.  Treat  with  a  mixture  of  nitric,  hydrochloric  and 
sulphuric  acid,  boiling  gently  in  a  covered  vessel  or  a 
mattrass,  until  decomposed  and  all  sulphur  is  oxidized; 
cool,  dilute,  filter  and  wash.  To  the  filtrate  and  wash- 
ings add  ammonia  in  excess;  filter,  wash  with  water  con- 
taining ammonia  until  it  gives  no  yellow  color  on  testing 
a  little  of  it  in  a  test-tube  with  a  glass  rod  moistened 


110  VOLUMETRIC    ASSAYS 

with  zanthate.  L3t  th3  eatlre  voIum3  of  solution  be 
about  half  a  pint,  adding  water  if  necessary  to  complete 
that  quantity,  then  proceed  with  the  zanthate  as  before. 
From  the  number  of  c.  c.  used,  and  the  titre  of  the  zan- 
thate, calculate  the  quantity  of  copper  in  the  assay,  as  in 
other  volumetric  methods,  and  froui  this  quantity  reckon 
the  percentage  on  the  weight  of  ore  taken. 

In  making  this  assay,  the  zanthate  should  at  first  be 
run  down  the  side  of  the  beaker,  to  prevent  frothing  and 
consequent  floating  of  the  p.  p.;  the  smaller  quantities 
added  toward  the  last  are  best  allowed  to  fall  upon  the 
stirring  rod  resting  in  the  beaker.  As  long  as  much  p. 
p.  is  formed,  it  may  be  plainly  seen  by  looking  down- 
ward on  the  solution,  but  the  faint  clouds  produced  later 
are  best  seen,  as  in  the  humid  assay  of  silver,  by  holding 
the  glass  toward  the  light,  and  looking  obliquely  upward 
through  the  liquid.  The  liquid  clears  better  if  there  is  a 
goodly  quantity  of  p.  p.  than  otherwise.  It  clears  best 
when  the  precipitation  is  near  completion.  Excessive 
stirring  is  disadvantageous  by  breaking  the  curd;  hence 
stir  but  little,  and  gentl3^  until  a  more  perfect  clearing 
becomes  necessary,  then  agitate  briskly  for  a  minute  or 
two,  and  settle  enough  to  leave  a  stratum  of  clear  liquid 
at  the  top  before  adding  more  zanthate.  After  this,  a 
very  slight  stirring  suffices. 

There  are  three  guides  to  the  ending:  Firstly,  the  dis- 
appearance of  the  green  color,  and  darkening  of  the  yel- 
low ;  secondly,  the  more  perfect  clearing,  and  thirdly,  the 
cessation  of  clouding  on  addition  of  zanthate.  To  make 
the  assay  well  some  practice  is  required ;  the  novice  is  al- 
most >ure  to  run  in  too  much  of  the  zanthate.     It  would 


OF  COPPER.  Ill 

be  quite  feasible  to  have  a  titrated  solution  of  copper 
with  which  to  work  back  by  adding  a  known  quantity, 
and,  in  the  final  reckoning,  deducting  a  corresponding 
weight  from  the  total  result.  The  most  convenient  way 
in  which  to  make  such  a  solution  is  to  dissolve  some  blue- 
stone  in  water,  and  then  titrate  a  certain  measure  of  the 
liquid,  which  should  be  quite  a  weak  solution.  To  use 
it,  measure  the  required  quantity,  add  ammonia,  and 
pour  the  whole  into  the  assay;  then  proceed  again  with 
zanthate. 

In  order  to  be  quite  sure  in  the  case  of  a  very 
complex  ore,  boil  the  first  acid  solution,  before  filtering, 
down  until  heavy  white  fumes  of  sulphuric  acid  come  off; 
cool;  add  a  little  water  and  a  piece  of  iron;  keep  the 
liquid  acid  with  sulphuric  acid,  and  digest  warm  until 
the  liquid  no  longer  stains  a  piece  of  clean  iron;  fil- 
ter, wash,  redissolve  the  precipitated  metals  in  mixed 
acids  as  before,  add  ammonia,  filter  and  proceed  with 
the  assay.  This  will  be  necessary  when  an  appreci- 
able quantity  of  cobalt  is  present  in  the  ore.  The  cop- 
per p.  p.  should  be  mustard  yellow  although,  with 
very  strong  zanthate,  it  may  appear  darker  at  first.  If 
it  is  distinctly  brown,  there  is  probably  cobalt  in  the  as- 
say, or  the  zanthate  may  be  out  of  order,  whicli  can  be 
tested  in  a  moment  by  means  of  some  ammoniacal  solu- 
tion of  copper. 

After  the  precipitation  of  the  copper,  a  very  slight  ex- 
cess of  zanthate  being  present,  if  acetic  acid,  added  to  the 
clear  liquid  in  slight  excess,  produces  a  reddish  yellow 
p.  p  ,  nickel  is  present ;  and  if  greenish  turbidit}-,  either 
at  once  or  on  further  addition  of  zanthate,  cobalt  is  also 


112  VOLUMETRIC   ASSAYS 

present,  and  another  portion  of  it  will  be  with  the  cop- 
per p.  p.,  spoiling  the  assay,  which  must  then  be  repeated 
as  directed  above.  By  again  adding  ammonia,  the  nickel 
p.  p.  is  redissolved  and  the  dirty  greenish  cobalt  p.  p. 
remains. 

Preparation  of  the  Potassium  Zanthate  Solu- 
tion.— Dissolve  two  ounces  (troy)  of  caustic  potassa  in 
about  a  quarter  pint  of  95  per  cent,  alcohol  in  a  stoppered 
bottle;  add  carbon  bisulphide,  little  by  little,  as  long  as  a 
curd  is  produced,  a  hissing  noise  heard,  and  a  partial  vac- 
uum is  formed  in  the  bottle,  as  evinced  by  the  stopper  re- 
sisting extraction.  Shake  the  bottle  occasionally.  When 
the  above  effects  cease,  and  a  further  addition  of  the  bi- 
sulphide causes  expansion,  which  may  expel  the  stopper, 
while  its  odor  is  no  longer  neutralized  but  becomes  disa- 
greeably perceptible,  and  a  yellowish  fluid  appears  which 
partly  liquifies  the  previously  almost  solidified  contents 
of  the  bottle,  pour  the  whole  into  a  dish  and  leave  it  to 
spontaneous  evaporation  in  a  dark,  cool  place  for  twelve 
hours  or  more.  The  dish  will  then  contain  a  pinkish, 
plastic  mass,  possessed  of  an  evil  odor.  Dissolve  this  in 
six  pints  of  cold  pure  water.  Let  the  solution  stand  a 
short  time  to  deposit  any  excess  of  bisulphide,  and  then 
bottle  it  in  common  beer  bottles  ("black  bottles")  which 
keep  in  a  cool,  dark  place. 

About  50  c.  c.  of  the  solution  thus  made  will  precipi- 
tate 0.5  gramme  of  copper.  It  may  be  diluted,  if  so  pre- 
ferred for  very  close  work,  so  that  it  will  require  100  or 
200  c.  c.  for  that  quantity  of  copper.  If  the  alcohol  is 
not  almost  saturated  with  caustic  potassa,  the  curdy 
mass  spoken  of  may  not  appear  until  evaporation  has 


OF   COPPER.  113 

taken  place.  The  compound  may  be  made  in  an  open 
dish,  the  carbon  bisulpliide  being  dropped  into  the  alco- 
holic solution  of  potassa  until  that  no  longer  reacts  alka- 
line, or  as  long  as  it  will  dissolve  by  stirring.  The  liquid 
is  then  left  to  evaporate. 

Regnault,  that  prince  of  chemists,  who  has  investigated 
almost  every  known  compound,  and  whose  name  is  con- 
stantly on  the  lips  and  pens  of  other  chemists,  says  that 
with  a  solution  of  absolute  alcohol,  the  greater  part  of 
the  potass  um  zanthate  falls  out  at  once  in  orange  col- 
ored crystals,  and  I  have  seen  it  so.  The  method  I  have 
given  is  that  which  I  use,  and  it  answers  my  purpose 
well.  The  solution  soon  decomposes  in  colorless  bottles, 
even  when  made  with  boile«l  water,  and  kept  with  exclu- 
sion of  air,  or  in  an  atmosphere  of  carbon  bisulphide;  in 
fact,  sooner  in  the  latter  case,  a  turbidity  appearing  at  the 
top,  and  gradually  spreading.  An  addition  of  potassium 
hydrate  produces  a  flocculent  precipitate,  after  the  set- 
tling of  which  the  liquid  remains  clear,  but  soon  becomes 
unfit  for  copper  assaying.  In  a  beer  bottle  it  remains 
clear  and  retains  its  properties  for  a  number  of  weeks. 
From  these  facts  it  is  inferred  that  light  is  the  chief 
cause  of  the  decomposition. 


114       ELECTROLYTIC  DETERMINATION 


ELECTROLYTIC  DETERMINATION  OF 
COPPER  IN  ORES,  ETC. 


[Contributed  by  Mr.  A.  K.  Brewer,  of  Tucson,  Arizona.] 
A  MOST  accurate  and  simple  determination  of  copper 
is  that  by  precipitation  from  a  nitric  acid  solution  upon 
platinum  foil,  by  means  of  the  electric  current.  The  ap- 
paratus required  is  a  battery  of  one  or  more  cells,  accord- 
ing to  amount  of  work  done,  a  few  platinum  cylinders 
and  spirals,  some  small  narrow  beakers  about  two  inches 
high,  porcelain  capsules,  etc.  A  very  satisfactory  type  of 
battery  is  Fuller's*  bichromate;  it  is  constant  as  well  as 
powerful.  The  chemicals  used  with  this  battery  are 
quicksilver,  bichromate  of  potash  and  sulphuric  acid. 

To  make  the  platinum  cylinder,  upon  which  the  copper 
is  to  be  deposited,  take  a  piece  of  platinum  foil  of  medium 
thickness,  two  by  two  and  a  half  inches,  and  with  the 
blow-pipe  solder  to  one  corner,  using  a  minute  fragment  of 
gold,  a  medium  thick  platinum  wire  three  inches  long. 
Then  roll  foil  into  a  cylindrical  or  a  spiral  form  of,  say, 
half  an  inch  in  diameter  and  two  inches  long.  For  the 
other  pole  take  a  platinum  wire  about  eight  inches  long, 
and  twist  three  inches  of  it  into  a  spiral  whose  outer  ring 

*0n  this  coast  Fuller's  battery  is  manufactured  only  by  the  Pacific 
Electrical  Works,  Sacramento,  Cal.,  and  sold  at  $2.50  per  large  cell. 


OF   COPPER   IN   ORES,    ETC.  115 

will  j  ust  fit  the  bottom  of  the  beaker ;  the  rings  turning 
inward  to  the  center  of  beaker,  when  the  wire  is  bent 
sharply  up,  so  that  the  spiral  will  sit  in  the  bottom  with 
five  inches  of  wire  extending  straight  up  through  the  cen- 
ter of  beaker.  Put  a  narrow  glass  tube  two  inches  long 
over  the  wire  so  that  it  rests  on  the  spiral  at  the  bottom. 
The  object  of  the  tube  is  to  prevent  contact  between  the 
cylinder  and  spiral  when  one  encircles  the  other. 

It  will  be  found  convenient  to  fasten  to  the  work-table 
two  parallel,  horizontal  brass  or  iron  rods  (thick  wire  will 
do)  about  fifteen  inches  long  and  three  inches  apart,  and 
raised  one  and  a  half  inches  from  the  table.  Between 
these  rods  are  placed  the  beakers;  in  this  manner  five  as- 
says or  more  may  be  carried  on  together  and  any  one  of 
them  can  be  detached  without  disturbing  the  others.  I 
have  been  using  four  cells  of  Fuller's  battery  and  can  run 
with  that  power  from  four  to  six  assays  at  a  time. 

The  zincs  and  carbons  are  coupled  alternately,  and  a 
wire  from  the  zinc  pole  is  attached  permanently  to  the 
left  hand  horizontal  rod;  wires  run  up  to  the  table  from 
each  carbon,  so  that,  by  connecting  the  first,  second,  third, 
or  fourth  carbon  with  the  right  hand  rod,  I  can  use  one, 
two,  three,  or  four  cells,  as  may  be  desired.  No  more 
current  should  be  used  than  is  necessarj^  for  a  strong  bat- 
tery may  cause  zinc  to  precipitate  on  the  foil. 

One  gramme  of  the  finely  pulverized  ore,  if  poor  in  cop- 
per, or  one-half  gramme,  if  rich,  is  treated  with  nitric  acid 
in  a  small  flask  until  complete  solution  of  the  copper  takes 
place,  then  excess  of  acid  is  evaporated  ofi*  until  residue  is 
only  just  covered  with  acid.  A  few  drops  of  sulphuric 
acid  are  add(3d  to  precipitate  lead,  and  the  mass  taken  up 


116  ELECTROLYTIC  DETERMINATION 

with  a  little  water.  The  solution  is  filtered  into  a  very 
small  bsaker  and  the  filter  washed  with  no  more  water 
than  is  necessary.  The  bulk  of  the  solution  is  preferably 
not  more  than  20  cubic  centimeters  (two-thirds  of  an 
ounce).  To  make  the  solution  uniform  it  is  stirred  with 
the  spiral  wire,  which  is  then  dropped  into  the  beaker. 
The  platinum  cylinder  is  put  over  this,  nearly,  but  not 
quite  touching  the  spiral  at  the  bottom.  Connections  are 
then  made  with  the  battery;  the  cylinder  being  joined  to 
the  zinc,  or  negative  pole,  and  the  spiral  to  the  carbon,  or 
positive.  Bubbles  will  rise  from  the  spiral  and  the  copper 
will  be  plated  upon  the  cylinder  in  a  thin  coherent  coat- 
ing which,  if  current  of  electricity  has  been  properly  reg- 
ulated and  amount  of  copper  in  solution  not  too  great, 
may  be  washed  without  the  slightest  danger  of  loss.  The 
solution  must  not  more  than  two- thirds  fill  beaker  nor 
must  the  cylinder  be  completely  covered.  When  solution 
becomes  perfectly  colorless,  a  little  water  is  added  to  beaker 
to  raise  the  level  of  the  liquid  and  so  expose  a  fresh  sur- 
face of  platinum  to  its  action.  If  no  further  deposit  is 
made  on  the  cylinder  the  precipitation  is  complete,  but  if 
a  film  of  copper  forms  upon  it  the  current  must  be  contin- 
ued until  no  more  copper  remains  in  solution.  The  cop- 
per is  all  precipitated  if  a  few  drops  of  the  liquid  on  a 
watch-glass  give  no  coloration  when  touched  with  a  drop 
of  sulphureted  hydrogen  water.  Now  slightly  acidulate 
some  water  with  sulphuric  acid  and,  without  interrupting 
current,  displace  liquid  in  beaker  with  the  acidulated 
water  by  pouring  it  into  a  funnel  which  touches  the  bot- 
tom of  beaker,  again  displacing  the  acidulated  liquid  with 
pure  water;  a  porcelain  dish  can  be  placed  under  beaker 
to  catch  the  liquid  which  overflows. 


OF   COPPER   IN   ORES,    ETC.  117 

The  cylinder  and  spiral  are  now  disconnected  from  bat- 
tery and  the  cylinder  put  into  a  porcelain  capsule  and 
washed  by  pouring  hot  water  over  it  twice  and  alcohol 
once.  The  capsule  is  then  heated  a  few  minutes  over  the 
water-bath  and  when  dry,  cooled,  and  the  copper  plated 
cylinder  weighed  on  an  assay  balance.  The  copper  is  dis- 
solved off  with  nitric  acid,  and  the  cylinder  washed,  dried, 
and  weighed.  The  difference  between  the  two  weights  is 
the  weight  of  copper  in  amount  of  sample  taken.  If  sev- 
eral cylinders  are  used  it  will  save  time  to  number  them 
and  record  their  weights,  as  then  it  will  nob  be  necessary 
to  weigh  them  every  time. 

Sometimes  new  foil  will  not  act  well ;  in  that  case  scour 
it  well  with  sea  sand  to  remove  the  outer  glaze,  and  if  that 
is  not  effectual,  a  few  minutes  treatment  with  nitro- 
hydrochloric  acid  will  remove  all  difficulty. 

If,  on  account  of  too  much  nitric  acid  having  been  used, 
the  copper  fails  to  precipitate,  the  acid  may  be  partially 
neutralized  with  carbonate  of  soda  and  the  solution  some- 
what diluted.  If  too  dilute,  or  too  little  nitric  acid  is 
present,  the  precipitate  will  be  spongy,  which  may  cause  a 
loss  of  copper.  Any  deposit  on  the  spiral  (lead,  manga- 
nese, etc.)  may  be  disregarded.  Metals  interferring  by 
being  deposited  with  the  copper,  are  silver,  antimony,  ar- 
senic, mercury,  and  bismuth.  Silver  may  be  removed  by 
the  addition  of  a  very  little  common  salt  to  the  nitric  acid 
solution  before  evaporating.  Every  trace  of  chlorine  must 
be  afterwards  driven  out  with  nitric  acid,  or  the  platinum 
cylinder  might  be  attacked  and  results  so  vitiated.  If 
the  solution  has  been  made  in  nitric  acid  only,  not  more 
than  a  trace  of  antimony  can  be  present.     Arsenic  is  not 


118  DETERMINATION  OF  COPPER  IN  ORES. 

frequently  deposited  on  the  copper,  but  even  when  it  is, 
all  the  copper  generally  comes  down  tirst,  when  the  cur- 
rent can  be  interrupted  and  the  arsenic  left  in  solution. 
It  may  be  advisable  sometimes  to  roast  ore  in  order  to 
volatilize  arsenic,  as  well  as  quicksilver.  Quicksilver,  if 
present,  would  be  deposited  as  a  white  coating  upon  the 
copper;  in  fact,  from  some  experiments  I  have  made,  I 
think  that  an  accurate  mercury  determination  can  be 
based  on  this  method.  Bismuth  is  not  of  frequent  occur- 
rence, but  if  present  must  be  removed.  It  may  be  precipi- 
tated from  the  solution  with  carbonate  of  ammonia,  the 
filtrate  evaporated  to  dryness,  ignited  to  remove  aaimo- 
nium  salts,  and  redissolved  with  nitric  acid,  etc.,  as  above. 
With  size  of  foil  given,  the  solution  should  not  contain 
more  than  0.4  gramme  copper;  so,  in  operating  upon  me- 
tallic copper,  borings,  etc.,  of  which  the  direct  solution  of 
a  small  amount  might  not  give  a  correct  average,  the  por- 
tion used  for  assay  should  be  obtained  by  dissolving  from 
2  to  10  grammes  of  the  sample,  filtering  into  a  measuring 
flask,  diluting  to  mark,  and  removing  with  a  pipette  from 
the  uniform  solution,  a  volume  containing  not  more  than 
0.4  gramme  pure  copper. 


TIN   ORES.  119 


TIN  ORES. 


Tin  stone  (tin  oxide)  is   readily  smelted  to  a  button. 

Take- 
Powdered  ore 1  part 

Potassium  Cyanide ...  J     " 

Soda J    " 

Mix;  put  in  pot;  heat  quickly.  When  fused,  leave  live 
minutes  in  fire;  then  shake,  tap,  allow  to  cool,  and  break 
the  pot.  The  button  is  silver  white,  malleable.  A  piece 
of  the  metal  boiled  in  nitric  acid  forms  a  white  powder  in- 
soluble in  water.  Antimony,  which  can  be  smelted  in 
the  same  way,  acts  similarly  in  nitric  acid.  But  anti- 
mony is  neither  white  nor  malleable.  It  is  gray,  crystal- 
fine,  and  brittle.     (See  Part  I  for  distinction.) 

The  presence  of  quartz  (silica)  causes  a  large  loss  of  tin 
in  the  smelting,  hence,  if  the  ore  is  not  pure,  it  should  be 
washed  by  "panning,"  or  vanning,  in  order  to  remove  the 
quartz  as  far  as  possible  from  the  heavier  tin  oxide  before 
smelting. 

Mixed  ores  containing  tin,  or  very  impure  tin  ores, 
should  be  boiled,  in  the  state  of  fine  powder,  in  a  mixture 
of   three  parts   hydrochloric   and  one  part   nitric  acid.* 

*From  Mitchell. 


120  ASSAYING   OF 

Heat  gently  for  half  an  hour,  then  boil  until  the  greater 
part  of  the  acid  has  evaporated.  Cool,  add  water,  settle, 
and  pour  the  water  off,  not  losing  any  solid  matter.  Wash 
thus  until  the  water  is  tasteless;  the  residue  is  tin  oxide, 
quartz  and  tungstic  and  if  the  ore  contained  tungsten,  as 
it  often  does.  The  tu  -gstic  acid  is  removed  by  gentle 
heating  for  an  hour  with  ammonia,  stirring  occasionally. 
The  ammonia  is  then  poured  off  and  the  residue  washed. 
The  quartz  is  removed  by  vanning,  and  the  tin  oxide 
smelted  as  before. 


MERCURY   ORES.  121 


MERCURY  ORES. 


The  principal  ore  of  mercury  is  the  red  cinnabar  for 
whic  1  red  iron-oxide  is  so  often  mistaken.  There  are  also 
black  ores  of  mercury,  and  many  silver,  copper,  and  other 
ores  contain  small  quantities  of  mercury. 

Before  assaying  a  doubtful  ore  for  mercury  it  is  well  to 
test  it.  Boil  some  of  the  powder  in  a  mixture  of  nitric 
and  hydrochloric  acid;  dilute  and  place  a  drop  of  the 
liquid  on  a  piece  of  gold.  Touch  the  gold,  through 
the  drop,  by  a  pointed  iron  or  steel  implement,  such  as  a 
penknife  or  a  needle.  If  the  ore  contained  a  trace  of  mer- 
cury, the  gold  will  be  instantly  amalgamated  on  that  spot, 
which  will  be  whitened.  Or  take  a  glass  tube  about  six 
inches  long  and  a  quarter  inch  diameter,  closed  at  one 
end;  place  in  the  tube  about  a  grain  of  the  ore  mixed 
witn  two  or  three  grains  of  litharge.  In  order  to  get  the 
charge  to  the  bottom  or  closed  end  of  the  tube  without 
soiling  the  other  part,  line  the  tube  with  a  rolled  slip  of 
writing  paper  (or  glazed  paper),  introduce  the  charge  and 
tap  it  down,  then  remove  the  paper.  Heat  the  end  of  the 
tube  containing  the  charge  in  the  flame  of  a  spirit  lamp, 
or  a  candle.  If  mercury  is  present,  it  will  first  evaporate, 
and  then  condense  in  the  cool  part  of  the  tube,  in  the  form 
of  minute  globnlfs  which  appear  like  a  mist  if  the  quan- 
9 


122  ASSAYING  OF 

tity  is  very  small.  Cut  the  tube  a  little  by  a  file  near  the 
charge,  and  break  off  the  part  containing  the  mercury. 
By  means  of  a  wire  and  a  bit  of  moist  cotton  cloth,  wipe 
the  interior  of  the  tube.  The  globules  of  mercury  will  be 
visible  on  the  swab,  by  the  aid  of  a  magnifying  glass,  or 
may  be  washed  off  in  a  cup  of  water.  By  weighing  the 
ore,  using  a  longer  tube  kept  cool  by  a  moist  cloth  toward 
the  open  end,  and  carefully  collecting  and  weighing  the 
mercury,  the  operation  becomes  an  assay. 
The  assay — 

Ore 1  part 

Lime 1-3  " 

Charcoal 1-10  " 

Mix ;  put  into  an  iron  or  clay  retort ;  cover  with  lime  and 
charcoal ;  close  the  retort  and  heat  to  bright  redness,  keep- 
ing the  retort  pipe  cooled  by  a  stream  of  water  flowing 
onto  a  cloth  wrapped  around  it.  Receive  the  condensed 
mercury  in  a  vessel  of  water  placed  under  the  end  of  the 
pipe.  The  pipe  should  not  dip  into  the  water,  but  a  piece 
of  cloth  tied  around  it  may.  Iron  filings  or  borings  will 
answer  in  place  of  lime.  Use  one  part  to  two  of  ore  for 
the  mixture,  and  some  more  as  a  cover.  Any  mercury 
which  may  remain  in  the  pipe  must  be  washed  out. 
Pour  the  water  off  from  the  mercury ;  dry  that  by  means 
of  filter  paper,  weigh,  and  report  in  percentage  of  the 
weight  of  ore  taken. 

A  small  assay  may  be  made  in  a  tobacco  pipe  used  as  a 
retort,  being  closed  by  means  of  clay.  A  small  amalgam 
reiort  is  suitable.  A  quicksilver  flask  with  a  pipe  adapted 
will  answer  for  several  pounds  of  ore.  The  flask  should 
be  previously  heated  to  redness  to  drive  out  any  quick- 


MERCURY  ORES.  123 

silver  which  may  be  adhering  to  it,  owing  to  its  having 
contained  quicksilver  before.  Gaspipe  alone  may  be  em- 
ployed. A  shoit  piece,  plugged  at  one  end,  serves  to  re- 
ceive the  charge,  and  this  is  connected  by  a  sleeve  with  a 
longer  piece.  It  is  better  if  the  short  piece  is  of  the 
greater  diameter,  say  two  inches,  and  connected  by  a  re- 
ducer with  a  longer  piece  of  f-inch  pipe.  When  the  dis- 
tillation is  finished,  the  pieces  are  disconnected  and  the 
longer  one  washed  for  recoverv  of  any  adhering  mercury. 


124  ASSAYING   OF 


ZINC  ORES, 


General  Method  for  all  Ores. — Treat  from  10  to 
100  grains,  or  a  suitable  number  of  grammes  of  the  finely 
powdered  ore  with  equal  parts  of  nitric,  hydrochloric,  and 
sulphuric  acid,  added  one  after  the  other  in  the  order 
named,  in  a  porcelain  vessel  covered  as  usual,  or  in  a  mat- 
trass.  Boil  until  heavy  white  fumes  come  off;  cool,  di- 
lute, cover  and  pass  in  a  stream  of  hydrogen  sulphide  un- 
til the  liquid  retains  the  smell.  If  arsenic  is  present,  the 
solntion  must  be  boiled  for  some  time  with  a<ldition  of 
sodium  sulphite  and  kept  acid  by  adding  hydrochloric 
acid;  otherwise,  zinc  will  ^o  down  with  the  arsenic.  Set 
it  in  a  wai'm  place  until  settled.  Filter,  and  wash,  with 
water  containing  hydrogen  sulphide,  as  quickly  as  possi- 
ble. Boil  the  liquid  until  it  no  longer  gives  off  an  odor 
of  hydrogen  sulphide;  add  a  little  nitric  acid  and  again 
boil.  To  the  hot  liquid  add  a  few  more  drops  of  nitric 
acid;  if  a  dark  shade  is  produced,  more  nitric  acid  is 
required.  Boil  down  considerably,  and  if  any  sulphur  is 
seen,  oxidize  it  by  a  few  crystals  of  potassium  chlorate, 
or  by  boiling  down  with  nitric  acid.  Cool;  add  am- 
monia in  considerable  excess.  Filter,  and  wash  with 
water  containing  ammonia  as  long  as  the  drippings  give 
a  p.  p.  with  ammonium  sulphide.     To  the   filtrate   add 


ZINC   ORES.  125 

hydrochloric  acid  until  it  reddens  litmus  paper,  and  then 
sodium  acetate  in  liberal  quantity. 

Again  pass  hydrogen  sulphide,  which  will  now  precipi- 
tate the  zinc  as  a  white  sulphide.  Settle;  collect  the  p.  p. 
on  a  filter  and  wash  with  water  containing  hydrogen  sul- 
phide. Dissolve  the  p.  p.  by  pouring  hob  dilute  hydro- 
chloric acid  upon  it,  a  little  at  a  time,  keeping  it  covered 
by  a  plate  of  glass,  or  better  by  a  small  funnel  inverted. 
Wash  the  cover  and  filter  with  hot  water.  All  the  liquid 
is  to  be  received  in  a  clean  beaker. 

The  treatment  now  depends  on  whether  the  last  p.  p. 
was  purely  white  or  mixed  with  black  sulphide  arising 
from  the  presence  of  nickel  or  cobalt  in  the  ore,*  or,  more 
likely,  from  imperfect  separation  of  copper  at  anearlierstage. 
In  the  first  case,  heat  the  liquid  and  add  solution  of  sodium 
carbonate  as  long  as  it  produces  a  p.  p.  Collect  the  p.  p. 
which  is  zinc  hydrocarbonate,  on  a  filter,  and  wash  it  with 
hot  water  as  long  as  the  drippings  cause  turbidity  in  a  lit- 
tle neutral  solution  of  copper  sulphate  (bluestone),  in  a  test- 
tube.  Dry  the  filter  with  its  contents;  transfer  the  latter 
to  a  porcelain  dish,  and  calcine  thoroughly  at  a  red  heat, 
which  converts  it  to  zinc  oxide.  Weigh,  and  calculate 
80.2  per  cent,  as  zinc.  In  the  second  case,  add  solution 
of  caustic  potassa  or  soda  in  excess,  which  will  redissolve 
the  zinc  oxide  at  first  precipitated,  leaving  the  other  metals 
insoluble.  Filter,  and  wash  till  the  drippings  no  longer 
blue  litmus  paper.  Acidulate  the  filtrate  with  hydro- 
chloric acid,  add  sodium  carbonate,  and  finish  as  in  the 
first  case. 


*  The  precipitation  of  nickel  and  cobalt  may  be  prevented  by  addi- 
tion of  citric  acid. 


126  ASSAYING   OF 

A  chemist  can  modify  and  simplify^  this  process  in  the 
absence  of  certain  metals,  such  as  copper,  arsnnic,  manga- 
nese, but  these  metals  are  frequent  companions  of  zinc  in 
our  silver  and  lead  ores,  and  it  is  solely  on  account  of  the 
influence  of  zinc  on  the  selling  price  of  these  ores  that  I 
have  thought  it  best  to  treat  of  the  assay  of  that  metal, 
which  has  no  market  value  in  such  ores.  As  it  would  oc- 
cupy too  much  space  to  give  all  the  modifications  applicable 
to  different  zinc  ores,  that  process  is  given  which  is  be- 
lieved to  cover  all  cases. 

The  trouble  of  igniting  the  p.  p.  may  bd  avoided.  Pro- 
ceed as  directed  up  to  the  point  at  which  the  precipitated 
zinc  sulphide  has  been  dissolved  in  hydrochloric  acid.  To 
the  solution  add  ammonia  in  excess,  then  hydrochloric 
acid  until  it  very  slightly  reddens  litmus  paper.  Now 
add  solution  of  sodium  phosphate  as  long  as  a  p.  p.  is  pro- 
duced. Heat  nearly  to  boiling  until  the  p.  p.  settles. 
Filter;  wash  with  hot  water  until  the  drippings  no  longer 
cause  turbidity  in  solution  of  silver  nitrate.  Dry  at  heat 
of  boiling  water  (on  the  water-bath);  remove  from  filter; 
weigh.  It  com 's  off  the  filter  beautifully.  Calculate 
36.89  per  cent,  of  the  weight  as  zinc. 

New  Method. — This  has  given  very  fair  results.  Dis- 
solve a  weighed  quantity  of  the  ore  as  directed  for  the 
new  copper  assay,  removing  arsenic  by  magnesium  mixt- 
ure if  but  little  iron  is  present,  using  ammonia,  regardless 
of  the  presence  of  manganese.  To  the  filtered  ammoni- 
acal  solution  add  potassium  zanthate  as  long  as  a  p.  p.  is 
formed.  Filter  and  wash.  To  the  liquid  add  ammo- 
nium sulphide  as  long  as  a  p.  p.  is  produced.  (The  p.  p 
should  be  white,  if  not,  proceed  as  in  similar  case  where 


ZINC   ORES.  127 

hydrogen  sulphide  is  used.)  Filter,  and  wash  with  water 
containing  a  little  ammonium  sulphide,  and  lastly  with 
hot  water.  Dissolve  the  zinc  sulphide  in  warm  dilute 
hydrochloric  acid,  saturate  with  ammonia,  again  add 
hydrochloric  acid  to  faint  acid  reaction,  then  sodium  phos- 
phate, etc.,  as  before. 


128  NEW   ASSAY    OF 


NEW  ASSAY  OF  NICKEL  AND  COBALT. 


Nickel  and  cobalt  usually  occur  together.  The  sub- 
stance may  contain,  besides  these  metals,  iron,  mano^anese, 
zinc,  copper,  gold,  silver,  lead,  bismuth,  antimony,  tin,  ar- 
senic, tellurium,  calcium,  barium,  strontium,  aluminum, 
magnesium,  silica  and  sulphur.  Should  it  also  contain 
mercury,  that  is  easily  expelled  by  calcination  of  the 
weighed  assay  before  proceeding  further. 

Powder  very  finely,  unless  the  substance  is  an  alloy, 
when  it  may  be  cut  or  rasped.  Take  ten  grains  or  one 
gramme,  or  less  if  the  substance  be  rich.  Digest  in  a 
plenty  of  nitrohydrochloric  acid,  the  nitric  in  excess.  Let 
all  sulphur  be  dissolved,  or  remove  the  drops  from  the  suf- 
ficiently cooled  liquid,  burn  them  in  a  small  basin,  dissolve 
the  residue,  and  add  it  to  the  main  solution.  Add  a  little 
sulphuric  acid,  unless  the  assay  contained  a  good  deal  of 
sulphur,  as  copper  or  iron  pyrites.  Evaporate  nearly  to 
dryness;  cool;  dilute;  filter;  wash  with  hot  water  until 
the  drippings  no  longer  give  a  dark  p.  p.  with  ammonium 
sulphide.  (Test  a  small  drop  on  white  porcelain.)  If  the 
volume  of  liquid  is  now  inconveniently  large,  reduce  it  by 
evaporation.  Add  solution  of  caustic  potassa  or  soda  very 
carefully,  nob  producing  any  distinct  p.  p.,  although  in 
many  cases  a  slight  turbidity,  but  the  liquid  must  remain 
acid  to  test  paper. 


NICKEL   AND   (COBALT.  129 

If  too  much  alkali  be  added,  it  must  be  counteracted  by 
a  drop  or  two  of  hydrochloric  acid ;  it  is  better  to  use  no 
alkali  than  too  much. 

Now  add  moist  precipitated  zinc  carbonate;  stir,  and 
continue  adding  the  carbonate  until  a  considerable  excess 
of  it  remains  unchanged  in  the  liquid,  which  may  be 
slightly  warmed.  If  the  assay  contained  no  copper,  test 
a  minute  drop  on  white  porcelain,  with  a  drop  of  solution 
of  potassium  sulphocyanide;  when  this  gives  no  red  or 
pink  tinge,  the  iron  is  all  down.  If  copper  is  present, 
test  for  that,  in  the  same  way,  with  potassium  ferrocy- 
anide,  which  will  give  a  brownish  red  color  as  long  as  any 
copper  remains  in  solution.  As  the  iron  goes  down  first, 
it  is  not  necessary  to  test  for  that  when  copper  is  present ; 
when  the  copper  is  all,  or  nearly  all  down,  a  bluish  or 
greenish  p.  p.  may  be  produced  by  this  test,  which  must 
not  be  mistaken  for  the  blue  which  a  persalt  of  iron 
would  produce;  it  is  caused  by  cobalt  or  manganese. 

When  the  copper  is  all  down,  filter,  and  wash  with  hot 
water  as  long  as  the  drips  give  a  p.  p.  with  solution  of  po- 
tassium zanthate.  (Return  these  tests  to  the  filtrate.) 
For  a  final  test  of  the  washings,  place  a  drop  on  porcelain 
and  add  a  drop  of  ammonium  sulphide;  it  should  not 
blacken.  Now  warm  the  liquid  to  about  blood  heat,  or 
a  little  higher,  and  add  solution  of  potassium  zanthate; 
stir,  and  continue  adding  the  zanthate,  at  intervals,  as 
long  as  it  is  seen  to  produce  a  yellow  or  a  greenish  p.  p. 
Keep  the  liquid  warm,  and  let  it  stand  some  time,  stirring 
occasionally,  until  it  clears  tolerably.  Try  a  little  more 
zanthate;  it  will  probably  make  a  white  p.  p.  of  zinc 
zanthate  which,  however,  either  changes  its  color  or  disap- 


130  NEW   ASSAY   OF 

pears,  being  either  converted  to  nickel  or  cobalt  zanthate, 
or  dissolved.  At  last,  filter  a  little  of  the  solution,  on  a 
filter  which  has  been  exactly  balanced  with  another  on  a 
fine  balance.  Test  the  filtered  liquid  with  potassium  zan- 
thate; if  any  yellow  or  green  p.  p.  forms,  return  the  test 
to  the  main  solution,  and  add  more  zanthate  to  that. 

When  no  more  p  p.  forms,  or  only  a  wliite  one  which 
dissolves,  make  a  fiaal  test  of  a  drop  with  ammonium  sul- 
phide; it  should  give  no  black  p.  p.  although  a  white  one 
of  zinc,  perhaps  tinged  by  pinkish  manganese  sulphide. 
Collect  the  p.  p.  after  letting  it  settle,  on  the  same  filter 
that  was  used  in  testing.  Any  p.  p.  which  may  adhere 
to  the  side  of  the  beaker  must  be  removed  by  the  aid  of 
hot  water  and  a  rubber  tipped  glass  rod.  A  short  piece 
of  pure  rubber  tube  on  the  end  of  the  rod  will  answer. 
Wash  several  times  with  hot  water. 

Place  a  clean  beaker  under  thi  filter,  and  leach  the  p.  p. 
with  slightly  diluted  ammonia  until  that  passes  colorless, 
and  a  drop  of  it  giv^es  no  p.  p.  with  a  drop  of  acetic  acid 
(or  very  dilute  sulphuric)  enough  to  destroy  the  smell  of 
the  ammonia.     (Return  the  drop,  if  it  gives  a  p.  p.) 

Remove  the  beaker  containing  the  ammoniacal  solution 
of  nickel  zanthate,  and  wash  the  cobalt  zanthate  on  the 
filter  with  hot  water  containing  a  little  ammonia,  until 
the  filter  is  clean  and  the  p.  p.  separates  well  from  it 
under  the  jet.  Dry  the  cobalt  zanthate,  still  on  the  filter, 
and  the  counterpoise  filter  with  it.  on  the  water-bath; 
cool  and  weigh  it,  on  the  filter,  putting  the  counterpoise 
filter  on  the  weight  pan;  return  both  to  the  water-bath 
for  ten  minutes;  cool  and  weigh  again,  and  so  until  it 
weighs  twice  alike. 


NICKEL   AND   COBALT.  131 

The  cobalt  zanthate  should  be  of  a  dark,  pure,  but  not 
brilliant  green  color.  If  mixed  with  mustard  yellow,  it 
contains  a  considerable  proportion  of  copper.  When  cal- 
cined, it  should  be  black,  not  green,  which  indicates  the 
presence  of  zinc;  and  if  it  gives  a  blue  solution  with  am- 
monia, copper  is  pre^^ent.  The  copper  may  be  'removed 
thus:  Redissolve  the  calcined  p.  p.  and  the  burned  filter,  in 
aqua  regia;  dry  with  addition  of  hydrochloric  or  sulphuric 
acid;  take  up  with  water  and  a  little  of  the  same  acid; 
digest  warm  with  a  piece  of  zinc,  keeping  the  liquid  dis- 
tinctly acid  so  that  bubbles  rise  from  the  zinc.  The  cop- 
per will  be  precipitated.  Remove  the  zinc  and  copper, 
nearly  neutralize  the  Uquid  by  potassa,  reprecipitate  the 
cobalt  by  potassium  zanthate,  wash,  dry  an<l  weigh. 

To  the  ammoniacal  solution  of  nickel  zanthate,  add  very 
dilute  sulphuric  acid  until  the  greater  part  of  the  nickel 
zanthate  is  reprecipitated,  but  the  liquid  still  smells  of  am- 
monia; then  add  acet.c  acid  until  the  liquid  has  a  slight 
acid  reaction.  Stir,  to  curdle  the  p.  p. ;  let  stand  for  some 
time,  stirring  occasionally.  Add  a  little  potas.sium  zan- 
thate, and  if  it  produces  a  p.  p.  add  as  much  more  as  may 
be  nexssary,  but  avoid  great  excess.  Filter,  cleaning  the 
beakei-  as  with  the  cobalt;  wash  with  hot  water  until  the 
p.  p.  cleaves  readily  from  tiie  filter  under  the  jet.  Dry 
on  the  water-bath ;  transfer  from  the  filter  to  the  weigh- 
ing capsule;  weigh;  place  the  capsule  with  the  p.  p.  on 
the  water-bath  for  15  minutes;  cool,  weigh,  and  so  on 
until  it  weighs  twice  aUke.  A  tared  or  counterpoised  fil- 
ter may  be  used,  as  with  the  cobalt,  but  the  nickel  zan- 
thate generally  comes  off'  the  filter  cleanly  if  well  washed. 

Each  of  the  zanthates  contains  19.6  per  cent,  of  metal 


13r2  NEW  ASSAY   OF 

or,  the  weight  multiplied  by  .196  is  the  weight  of  the 
nickel  or  cobalt.  The  filtrations  may  be  greatly  facili- 
tated by  connecting  a  foot  of  rubber  tubing  to  the  beak 
of  the  funnel  and  letting  it  hang  downward,  the  end  in 
the  receiving  vessel.  This  should  not  be  done  while  leach- 
ing with  ammonia. 

In  certain  circumstances,  believed  to  be  the  presence 
of  arsenic  in  the  solution,  the  precipitation  of  copper  by 
zinc  carbonate  is  not  quite  complete.  If,  however,  there 
is  sufficient  iron  present,  the  difficulty  no  longer  exists; 
hence,  if  a  little  copper  should  remain  in  solution,  notwith- 
standing an  excess  of  zinc  carbonate,  add  a  little  iron  per- 
chloride,  as  nearly  neutral  as  may  be,  and  then  more  zinc 
carbonate  if  necessary.  If  the  ore  is  known  to  contain 
arsenic,  with  but  little  iron,  while  copper  is  also  present, 
it  may  save  trouble  to  add  a  little  metallic  iron  to  the 
acid  solution,  before  treating  it  with  zinc  carbonate,  and 
digest  warm  until  the  iron  is  dissolved.  In  this  way  the 
quantity  of  copper  in  the  solution  is  reduced  and  that  of 
iron  augmented.  The  liquid  must  be  kept  distinctly  acid 
during  this  operation,  so  that  bubbles  of  gas  rise  constantly 
from  the  iron.  The  iron  must  be  peroxidized.  In  the 
treatment  with  zinc  carbonate,  the  liquid  may  be  slightly 
warmed,  not  highly  heated. 

The  potassium  zanthate  made,  as  directed  for  the  copper 
assay,  with  alcohol  of  95  per  cent,  or  thereabout,  is  a  little 
alkaline,  and  becomes  more  so  by  keeping.  In  this  state  it 
is  not  fit  for  this  assay.  Before  using  it,  test  it  with  faintly 
reddened  litmus  paper ;  if  it  blues  that,  add  some  very  di- 
lute sulphuric  acid,  not  strong  enough  to  cause  turbidity, 
or,  if  it  does  bo,  warm  the  liquid  until  clear.     Or,  add 


NICKEL   AND   COBALT.  188 

carbon  bisulphide  and  alcohol  to  dissolve  it  until  the  liquid 
is  neutral. 

To  make  the  zinc  carbonate,  or  rather  hydrocarbonate, 
dissolve  zinc  sulphate  in  water,  and  filter  it.  Also  dis- 
solve sodium  or  potassium  carbonate  in  water.  Filter  the 
latter  into  the  former  until  nearly  but  not  quite  all  the 
zinc  is  thrown  down.  Collect  the  p.  p.  on  a  filter  and 
wash  it.  The  filtrate  should  still  give  a  slight  p.  p.  on  ad- 
dition of  the  soda  solution  in  order  to  guard  against  an 
excess  of  soda,  which  would  be  difficult  to  wash  out  of  the 
zinc  carbonate.  Keep  the  carbonate  moist  in  a  wide- 
mouthed  jar  or  bottle. 

Resume  of  Operations. 

1.  Dissolve;  dry;  take  up;  filter.* 

2.  Treat  with  zinc  carbonate;  filter. 

3.  Precipitate  with  potassium  zanthate;  filter. 

4.  Leach  with  ammonia. 

5.  Dry  and  weigh  cobalt  zanthate. 

6.  Recover  nickel  zanthate  by  acid;  filter,  wash,  dry, 
weigh. 

7.  Multiply  weights  by  .196  for  metal.  If  the  greatest 
possible  accuracy  is  required,  see  Fresenius  Quan  An,  or 
send  the  assay  to  an  analytical  chemist. 

"  While  working  up  this  assay,  I  was  informed  that 
a  Mr.  Phipson,  in  1877,  had  published  an  account  of  the 
precipitation  of  nickel  and  cobalt  by  potassium  zanthate, 
and  the  separation  of  the  zanthates  by  ammonia.  So 
far  as  I  know,  however,  Mr.  Phipson  did  not  determine 
the  metals  quantitatively  as  zanthates,  nor  apply  his 
method  to  the  assay  of  ores. 

*  This  filtration  may  probaMy  be  omitted  without  injury. 


134      NEW  ASSAY  OF  NICKEL  AND  COBALT. 

"  As  ]  wish  to  be  perfectly  fair  and  honest  in  these 
matters,  I  will  state  that  my  knowledge  of  the  different 
behavior  of  nickel  and  cobalt  zanthates  toward  am- 
monia was  the  result  of  experiments  made  by  Mr.  G.  F. 
Beardsley,  in  consequence  of  some  information  I  had 
given  him  on  copper  and  nickel  zanthates. 

"  Conceiving  the  idea  that  the  reactions  might  be  made 
use  of  in  the  assay  of  the  three  metals,  I  took  the  first 
opportunity,  which  did  not  occur  until  some  years  later, 
of  working  them  up,  with  the  results  given  in  this  book. 
My  main  object  was  to  avoid  the  use  of  hydrogen  and 
amnonium  sulphides. 

*'  I  am  not  aware  that  the  copper  assay  by  zanthate 
lias  ever  been  attempted  before,  and,  taking  my  assay  of 
nickel  and  cobalt  as  a  whole,  it  is  certainly  original,  and 
I  think  myself  justified  in  calling  it  new." 


ASSAY   OF    CHROMIUM.  135 


ASSAY  OF  CHROMIUM. 


This  assay  is  not  for  every  substance  which  may  con- 
tain chromium,  but  for  chrome  ore  proper.  Powder  as 
finely  as  possible.  Take  5  grains  or  half  a  gramme. 
Fuse  in  a  platinum  crucible  with  2  parts  of  nitre  and  4  of 
soda,  or  better  with  dried  caustic  soda  alone.  Add  the 
soda,  etc.,  a  little  at  a  time,  and  stir  with  a  stout  platinum 
wire.  Cool,  and  dissolve  in  hot  water  (put  crucible  and 
all  into  the  dish),  filter;  acidulate  with  hydrochloric  acid; 
add  alcohol  and  boil  until  the  liquid  becomes  quite  green. 
Precipitate  by  ammonia,  and  boil.  Filter  while  hot,  and 
wash  with  hot  water.  Dry  the  p,  p. ;  burn  the  filter,  and 
add  the  ashes  to  the  p.  p.  Ignite  the  whole.  Weigh ;  de- 
duct the  weight  of  the  ashes  of  a  similar  filter.  Report 
as  so  much  per  cent,  chromium  sesqiiioxide,  which  is  what 
the  p.  p.  consists  of.  The  stirring  with  platinum  wire 
during  the  fusion  often  prevents  the  need  of  a  second  fu- 
sion, butlif  any  ore  remains  insoluble,  that  portion  must 
be  collected,  dried,  and  fused  with  a  fresh  quantity  of 
soda,  etc. 

The  platinum  crucible  must  not  come  in  contact  with 
the  fuel,  therefore  put  it  inside  of  a  common  assay  cruci- 
ble and  pack  lime  around  it. 


136  ASSAY   OF 


ASSAY  OF  BISMUTH. 


SmeI-T  a  suitable  quantity  of  the  powdered  ore  in  an 
assay  crucible,  with  borax  and  a  mixture  of  equal  parts 
Df  soda  and  potassium  cyanide.  Copper  may  be  kept 
out  of  the  button  almost  entirely  by  means  of  sulphur 
or  arsenic;  hence,  if  the  ore  contains  copper,  and  little 
arsenic  or  sulphur,  or  none,  add  sulphur  and  powdered 
charcoal  in  the  dressing,  also  a  couple  of  nails.  In  this 
way  the  bismuth  can  be  got  tolerably  pure  from  very 
complex  ores  containing  copper,  zinc,  nickel,  cobalt,  and 
tellurium.  Gold  and  silver,  if  present,  will  go  into  the 
button,  which  should  therefore  be  cupelled  after  weigh- 
ing, and  the  weight  of  precious  metal  found  deducted. 

Lead  and  antimony,  if  present,  will  go  into  the  button. 
With  very  poor  ores,  it  is  even  advisable  to  add  some 
litharge  in  the  dressing,  in  order  that  the  resulting  lead 
may  collect  the  bismuth.  About  4  times  the  weight  of 
the  bismuth  will^  suffice.  In  these  cases,  or  if  much 
copper  has  been  allowed  to  go  into  the  button,  that  must 
be  purified.  Laminate  or  powder  it,  according  as  it  is 
tough  or  brittle,  and  digest  it  in  boiling  nitric  acid,  which 
must  be  considerably  diluted  if  lead  is  present.  This 
will  dissolve  the  bismuth,  lead,  copper,  and  silver,  leaving 
antimony  (and    tin)    insoluble.     Add   enough    sulphuric 


BISMUTH.  137 

acid  to  precipitate  the  lead;  boil  off  some  of  the  acid; 
cool;  add  water  and  boil.  If  thtre  is  any  insoluble 
matter,  settle;  decant  onto  a  filter;  boil  again  two  or 
three  times  with  water  and  a  little  sulphuric  acid,  also  a 
drop  of  nitric  acid,  decanting  each  time  onto  the  filter. 
Finally  throw  the  residue  onto  the  filter  and  wash  it 
slightly;  it  should  be  tested  by  blowpipe  for  bisnmth 
which  should  not  be  found. 

To  the  filtrate,  in  a  large,  covered  beaker,  add  excess 
of  ammonium  carbonate;  heat  to  boiling;  filter;  wash 
with  w^ater  containing  ammonia  until  that  passes  color- 
less. Dry;  remove  the  p.  p.  from  the  filter,  which  burn. 
Smelt  the  p.  p.  and  the  filter  ash  together,  with  a  little 
borax  glass  and  potassium  cyanide,  in  a  small  crucible. 
Cool  and  break  the  pot;  separate  the  button  from  the 
slag  with  care;  it  may  be  cleaned  by  means  of  warm 
water  with  a  little  sulphuric  or  hydrochloric  acid. 
10 


138  ASSAY    OF   ARSENIC. 


ASSAY  OF  ARSENIC. 


In  a  porcelaiQ  crucible  fuse  half  a  gramme  (or  less  if 
rich)  of  the  powder  with  6  to  10  parts  of  a  mixture  of  so- 
dium carbonate  and  nitre  (in  equal  parts).  Coot;  ex- 
tract with  water  warmed  in  the  crucible;  filter.  The 
filtrate  contains  the  arsenic  combined  with  alkali.  .  Acid- 
ify with  nitric  acid,  and  boil.  Cool;  neutralize  almost 
exactly  by  ammonia,  so  that  previously  reddened  litmus 
shows  alkali  in  half  a  minute.  If  not  clear,  filter.  Add 
solution  of  neutral  silver  nitrate  (lunar  causiic)  in  slight 
excess.  Stir  to  coagulate  the  p.  p.,  which  is  of  a  brick 
red  color.  Filter;  wash  the  p.  p.  with  cold  water.  Test 
the  filtrate  with  silver  nitrate,  dilute  nitric  acid  and  am- 
monia (to  again  neutralize),  in  order  to  see  that  precipita- 
tion IS  complete.  Scorify  the  p.  p.  with  lead,  and  cupel 
the  button. 

If  the  ore  contained  any  chlorides,  as  silver  chloride,  etc., 
instead  of  at  once  scorifying  the  p.  p.  pour  dilute  nitric 
acid  on  it,  on  the  filter,  to  dissolve  it  and  separate  it  from 
silver  chloride  which  will  remain  on  the  filter.  To  the 
liquid  add  enough  hydrochloric  acid  to  piecipitate  all  the 
silver  in  that  as  chloride,  which  collect  on  a  filter,  wash 
with  hot  water,  dry  and  scorify  with  load,  adding  a  little 
soda.  Calculate  the  arsenic  from  the  silver  got,  in  the 
ratio  of  648  of  silver  to  150  of  arsenic. 

The  writer  has  not  tried  this  method,  but  it  seems  to  be 
a  good  one.  It  is  stated  that  phosphorous  and  molybde- 
unm  may  interfere. 


ASSAY  OF  ANTIMONY.  139 


ASSAY  OF  ANTIMONY. 


Fuse  a  weighed  quantity  of  the  powdered  ore,  in  a  clay 
crucible,  with  4  parts  potassium  c^^anide,  at  as  low  heat 
as  possible.  Cool  and  break  the  pot.  Carefully  separate 
the  slaof  from  the  button,  which  will  be  brittle  almost  in- 
variably.  If  the  ore  contained  little  or  no  other  reducible 
metal,  the  button  may  be  weighed  at  once  as  metallic  an- 
timony; otherwise,  as  in  the  presence  of  lead,  etc.,  powder 
it  if  brittle,  laminate  if  tough,  and  digest  with  rather  di- 
lute nitric  acid.  Nearly  all  of  the  antimony  will  remain 
as  a  white  powder  which,  w  hen  washed  with  hot  water, 
dried,  and  again  fused  with  potassium  cyanide,  will  yield  a 
button  of  metallic  antimony  (and  tin,  if  present,  which  is 
nob  probable). 

To  assay  an  alloy  of  antimony  and  tin,  dissolve  in  aqua 
regia  with  excess  of  hydrochloric  acid,  dilute  the  solution, 
adding  more  hydrochloric  acid  if  a  white  p.  p.  falls,  to  re- 
dissolve  that.  Place  a  piece  of  pure  tin  in  the  liquid,  keep 
warm,  and  maintain  a  slight  excess  of  hydrochloric  acid. 
Collect,  wash,  dry  and  weigh  the  precipitated  antimony. 
The  lost  weight  will  be  that  of  the  tin  in  the  alloy. 
These  methods  are  not  quite  exact  but  will  generally 
serve  the  purpose  of  the  assayer. 


140  ASSAY   OF   SULPHUR. 


ASSAY  OF  SULPHUR. 


Act  on  a  weighed  quantity  of  the  powdered  ore  with 
aqua  regia,  or  strong  nitric  acid  and  potassium  chlorate. 
If  some  sulphur  separates  in  clear  melted  drops,  cool 
sufficiently,  remove  the  solidified  drops  and  weigh  them. 
Evaporate  to  dryness,  adding  some  hydrochloric  acid 
toward  the  end.  Boil  with  strong  sohition  of  potassium 
carbonate,  or,  but  not  so  well  sodium  carbonate,  for  half 
an  hour.  Filter  and  wash;  acidulate  the  filtrate,  in  a 
large  beaker,  with  hydrochloric  acid,  add  solution  of 
barium  chloride  in  slight  excess.  Allow  to  settle  in  a 
warm  place  for  an  hour  or  more,  filter  on  a  fine  filter, 
wash  with  hot  water,  dry,  and  ignite  the  p.  p.  Weigh 
when  cold,  and  multiply  the  weight  by  0.137  for  weight 
of  sulphur.  Add  the  weight  of  any  sulphur  that  may 
have  been  weighed  as  drops.  If  barium  is  present,  fuse 
the  residue  in  a  platinum  crucible  with  5  parts  of  mixed 
sodium  and  potassium  carbonates;  cool;  dissolve  in  water, 
filter  and  wash.  Acidulate  the  liquid  and  add  it  to  the 
other. 


ASSAY   OF    SALT.  141 


ASSAY  OF  SALT. 


In  buying  salt  for  milling  purposes  it  is  often  desirable 
to  know  its  percentage  of  purity,  or  its  fineness. 

Take  542  parts  by  weight  (say  542  grain  or  gramme 
points  =  5.42  grains  or  0.542  gramme).  If  it  were  pure, 
it  could  convert  1,000=  10  grains  or  1  gramme  of  silver 
into  chloride.  Dissolve  in  water;  acidulate  slightly  with 
nitric  acid;  warm  and  add  solution  of  silver  nitrate;  stir 
to  curdling  of  the  p.  p. ;  settle  and  add  a  little  more 
silver  nitrate,  and  so  as  long  as  a  p.  p.  is  formed.  An 
excess  of  silver  nitrate  will  do  no  harm.  Settle;  filter; 
wash  with  hot  water  until  the  drippings  cause  no  p.  p. 
in  salt  solution.  Dry;  dtess  on  filter  with  litharge,  soda, 
and  borax  mixed.  Put  filter  and  all  into  a  crucible; 
smelt  and  cupel  as  in  an  ore  assay.  Weigh  the  resulting 
silver  bead,  adding  a  correction  for  cupel  lation  loss  ac- 
cording to  experience.  The  bead  weight  in  points  is  the 
fineness  of  the  sample,  and  that  divided  by  10  is  the 
percentage  of  pure  salt  (or  the  equivalent  of  that  for 
utility). 

Marsh  salt  often  contains  soda  or  lime,  and,  if  used  in 
conjunction  with  bluestone  or  acid,  as  in  working  silver 
ores  by  amalgamation,  renders  a  portion  of  these  useless. 
In  acidulating  the  solution  as  above,  observe  if  much 
effervescence  ensues,  as  it  may  be  better  to  pay  a  higher 
price  for  a  better  article. 


142  ASSAY   OF   SALT. 

To  find  how  much  bluestone  the  impure  salt  will  coun- 
teract, take  100  parts  (say  grains)  of  the  sample;  dis- 
solve in  water  and  add  10  parts  of  bluestone  also  dis- 
solved in  water.  Boil  for  a  few  minutes,  and  if  the 
liquid  is  decolored,  add  another  quantity  of  bluestone 
and  again  boil.  Filter  and  wash;  acidulj^e  the  liquid 
with  sulphuric  or  hydrochloric  acid;  precipitate,  wash 
and  weigh  the  copper  remaining  in  solution  exactly  as 
in  making  a  copper  assay  (or  determine  the  copper  by 
either  of  the  other  processes  given).  The  weight  of  the 
copper  multiplied  by  4.06  is  the  weight  of  bluestone  not 
made  useless  by  the  impurities  in  the  sample,  and  this 
d<!jducted  from  the  total  weight  of  bluestone  used  leaves 
the  weight  made  useless  by  100  of  the  sample.  The  blue 
crystals  of  bluestone  should  be  used,  rejecting  any  white 
portion. 

To  find  out  how  much  of  the  acid  in  use  the  material 
will  neutralize,  take  100  or  1,000  grains  of  the  sample; 
dissolve  in  water  and  heat  the  solution.  Take  also  a 
weighed  quantity  of  the  acid,  say  10  or  100  grains,  and 
pour  it  into  5  or  6  times  as  much  water;*  mix  and  weigh 
aerain,  or  measure  the  mixture,  if  more  convenient.  Add 
the  acid  liquid,  little  by  little,  to  the  salt  solution,  stirring, 
and,  when  effervescence  ceases,  testing  after  each  addi- 
tion with  blued  litmus  paper,  until  that  is  slightly  red- 
dened. The  proportion  of  the  dilute  acid  used  indicates 
the  proportion  of  the  acid  taken  which  was  necessary  to 
counteract  the  alkaline  matter  in  the  taken  weight  of 
the  sample. 

*N'ever  pour  water  into  stroag  acid,  but  pour  the  acid  iato  the  water 
to  avoid  explosion. 


APPENDIX   TO   PART   ONE.  143 


APPENDIX  TO  PART   I. 


A  NEAT  way  in  which  to  make  the  assay  of  gold  and 
silver  ores  containing  much  copper,  is  to  treat  the  weighed 
assay  with  strong  nitric  acid  until  the  copper  is  dissolved; 
filter  and  wash.  To  the  filtrate  and  washings  add  hydro- 
chloric acid  or  solution  of  common  salt  as  long  as  a  precipi- 
tate is  produced.  Collect  the  p.  p.  on  a  separate  filter  and 
wash  it.  The  whole  of  the  silver  will  be  on  the  filters, 
that)  portion  which  existed  in  the  ore  as  chloride,  iodide  or 
bromide  on  the  first,  the  remainder  on  the  second,  also 
converted  into  chloride.  It  will  not  answer  to  add  salt  or 
hydrochloric  acid  during  the  treatment  of  the  ore,  because 
the  proper  quantity  cannot  be  known,  and  an  excess 
would  cause  gold  to  be  dissolved  and  lost. 

Dry  the  two  filters  with  their  contents;  remove  them 
from  the  funnels;  dress  the  residue  from  the  ore  with 
litharge,  borax  and  soda  as  a  crucible  assay  by  the  first 
system,  proportioning  the  fluxes  to  the  quantity  of  sub- 
stance. If  there  should  be  much  separated  sulphur,  some 
nitre  may  be  needed.  Put  the  whole  into  a  crucible. 
Dress  the  other  filter  with  a  small  quantity  of  litharge 
and  soda,  and  put  it  also  in  the  pot.  In  adjusting  the 
fl,our  or  nitre,  it  must  be  remembered  that  the  filters  will 
act  as  reducers,  unless  indeed  they  have  been  burned  to 


144  APPENDIX   TO   PART   ONE. 

ashes  in  the  drying,  which  may  be  done  on  a  roasting 
dish  in  the  muffle  very  speedily.  Cover  with  salt,  and  on 
that  put  som-)  borax.  Melt  and  proceed  as  usual.  As- 
says made  in  this  way  work  very  cleanly  and  quickly,  as 
there  is  not  much  besides  quartz  and  silver  chloride  to 
melt.  The  method  has  not,  however,  usually  given  any 
better  results  than  others.  The  chief  advantaofe  is  that  a 
very  large  quantity  can  be  taken,  it  being  greatly  re- 
duced by  the  acid  treatment.  In  the  case  of  sulphuretted 
ores,  time  may  be  saved  by  roasting  the  weighed  assay 
before  dissolving  the  copper  out. 

In  assaying  coppery  ores  by  the  second  system,  it  should 
be  remembered  that  soda,  in  presence  of  carbon,  can  re- 
duce some  metallic  copper  from  the  sulphide,  for  which  rea- 
son Hour  or  charcoal  should  be  used  only  in  such  quantity 
as  to  deoxidize  the  litharge,  copper  oxide,  etc.  It  may  be 
omitted  entirely  if  enough  sulphur  is  present  or  added. 

For  concentrated  pyrites,  whether  concentrated  natur- 
ally or  artificially,  the  second  system  is  decidedly  prefer- 
able in  point  of  convenience.  In  assaying  this  class  of 
material  by  the  first  system,  using  nitre  to  counteract  the 
excess  of  reducing  matter,  it  may  happen  that,  although 
the  nitre  has  been  adjusted  in  accordance  with  the  indica- 
tions of  a  preliminary,  little  or  no  lead  is  got.  The  nat- 
ural supposition  then  is,  that  too  much  nitre  has  been 
used,  and  that  the  lead  remains  in  the  state  of  oxide. 
This  is  an  error.  The  lead  is  retained  not  by  oxygen  but 
by  sulphur.  On  repeating  the  assay  with  a  smaller  pro- 
portion of  nitre,  the  result  is  no  better  than  before,  while, 
if  it  be  made  with  a  larger  proportion,  the  apparently 
paradoxical  result  is  that  more  lead  is  got,  though  not  the 
full  quantity  called  for  originally. 


APPENDIX    TO   PART   ONE.  145 

This  thing  has  puzzled  many  an  assayer  and  is  under- 
stood by  very  few.  It  has  led  some  to  the  practice  of 
using  nails  in  a  nitred  assay  at  the  risk  of  getting  too 
much  lead,  and  of  forming  oxysulphides  in  the  slag,  which 
is  stated  on  good  authority  to  be  dangerous.  It  is  true 
that  I  have  suggested  tho  use  of  a  smfiall  quantity  of  nitre 
in  the  assay  of  such  ore  by  the  second  system,  but  the 
litharge  used  in  that  is  not  in  excess  of  the  quantity  of 
lead  required,  and  too  much  cannot  be  got,  while  the  lit- 
tle nitre  intended  to  be  used,  if  any,  is  only  enough  to 
burn  a  portion  of  the  excess  of  sulphur  which  exists  in 
iron  pyrites  beyond  what  is  required  to  retain  the  iron  in 
the  form  of  a  sulphide  containing  the  minimun  proportion 
of  sulphur,  to  which  condition  it  must  be  reduced  in  order 
to  ensure  the  extraction  of  the  precious  metal.  It  is  for 
this  purpose,  in  part,  that  nails  are  used. 

The  difficulty  spoken  of  is  caused,  not  by  an  excess  of 
nitre,  but  by  a  deficiency  of  litharge.  It  has  already 
been  stated  that  iron  pyrites  require  50  parts  of  litharge 
to  effect  complete  oxidation,  reducing  only  8  or  8^  parts 
of  lead,  that  is  very  much  less  than  the  entire  quantity  of 
lead  in  the  litharge.  The  reason  of  this  is,  that  when  lith- 
arge is  combined  with  a  certain  proportion  of  iron  oxide,  it 
loses  the  power  of  oxidizing  sulphurets.  When  the  ore 
consists  entirely  of  iron  pyrites  which,  in  this  class  of  as- 
say, must  be  completely  oxidized,  a  large  quantity  of  iron 
oxide  is  formed.  This  engages  a  corresponding  quantity 
of  the  litharge,  rendering  that  powerless  to  decompose  sul- 
phurets of  any  kind,  even  galena.  Now  suppose  we  use 
nitre  enough  to  oxidize  about  90  per  cent,  of  the  pyrites, 
the  remaining  10  per  cent,  (the  ore  being  all  pyrites)  re- 


146  APPENDIX    TO   PART   ONE. 

quire  50  times  as  inucii  litharge,  that  is  5  times  the  weight 
of  the  entire  assay.  Besides  this,  a  quanti:y  of  litharge 
is  required  to  combine  with  the  iron  oxide  produced  by 
the  action  of  the  nitre  on  90  per  cent,  of  the  pyrites,  oth- 
erwise the  10  per  cent  of  pyrites  cannot  be  oxidized,  be- 
cause the  litharge  intended  to  act  on  them  is  otherwise 
employed.  The  result  is  that  little  or  no  lead  is  got,  since 
little  or  no  litharore  is  reduced.  It  remains  in  the  slaof 
partly  combined  with  iron  oxide  and  partly  with  a  por- 
tion of  the  sulphur  of  the  10  per  cent,  of  the  pyrites. 

It  can  now  be  seen  why  more  nitre  may  cause  more 
lead  to  be  reduced  by  leaving  less  than  10  per  cent,  of  the 
pyrites  to  be  acted  on  by  the  litharge,  for,  although  more 
iron  oxide  is  produced,  it  does  not  consume  litharge  in  the 
same  proportion  as  is  required  by  the  pyrites.  The  re- 
maining quantity  of  the  latter  is  then  completely  oxidized, 
and  an  equivalent  quantity  of  lead  is  thrown  down.  If  a 
sufficient  quantity  of  litharge  had  been  used,  instead  of 
more  nitre,  the  10  per  cent,  or  so  of  pyrites  would  have 
been  oxidized,  and  the  calculated  quantity  of  lead  got. 
The  indications  of  a  well-made  preliminary  may  always 
be  relied  on  if  enough  litharge  is  used. 

From  the  foregoing  it  appears  that  the  assay  of  this 
class  of  ore  by  the  first  system,  using  a  graduated  quan- 
tity of  nitre,  must  require  even  more  than  the  5  pa^ts  of 
litharge  prescribed  for  all  ores  by  Mitchell,  and  this  is  true 
when  the  ore  is  all  pyrites.  But  it  seldom  happens  that 
even  concentrations  contain  more  than  80  per  cent,  of 
pyrites,  the  remainder  consisting  of  other  sulphurets, 
quartz,  etc.  Moreover,  as  has  been  stated  heretofore,  the 
presence  of  soda  and  silica,  forming  glass,  and  of  borax 


APPENDIX    TO   PART   ONE.  147 

also,  has  an  influence  because  these  combine  with  the  iron 
oxide,  releasing  a  corresponding  quantity  of  the  litharge, 
so  that  the  more  of  them  we  employ,  the  less  litharge  is 
necessary. 

For  well  concentrated  pyrites,  the  following  dressing  is 
suitable. 

Ore 1         part 

Nitre 1.7 

Litharge 8-10     '' 

Soda 1-2      " 

Borax 1  " 

Glass 1-1       " 

The  litharge  may  be  lessened  as  the  proportion  of  soda 
and  glass  is  increased. 

The  following  described  experiments  which  I  made  for 
the  purpose,  will  assist  in  understanding  the  facts  stated. 

1st.  Ore 12  grains 

Litharge 480      " 

Gave,  on  fusion,  63  grains  of  lead.  A  larger  proportion 
of  litharge  gave  no  more,  the  ore  not  being  pure  pyrites. 

2d.  Ore 12  grains 

Litharge 240      " 

Soda 240      '' 

Gave  also  63  grains  of  lead. 

3d.  Ore 12  grains  ♦ 

Litharge 240      " 

Gave  only  57  grains  of  lead  which  was  not  well  collected 
in  a  button. 


148  APPENDIX   TO   PART   ONE. 

4th.  Ore 12  grains 

Litharge 240      '* 

Glass 30     " 

Gave  61  grains  of  lead,  and  poured  cleanly. 
5th.  Ore 12  grains 

Litharge 120     " 

Soda 240     " 

Gave  47  grains  of  lead  which  was  a  good  deal  scattered. 
Reinelted  with  more  soda,  gave  48  grains  lead. 
6th.  Ore 12  grains 

Litharge 120 

Soda 120       " 

Glass 60       *' 

Gave  63  grains  of  lead  and  a  clean  pour. 
7th.  Ore 1 20  grains 

Nitre 180       '' 

Litharge.  .  ..  ....  240       " 

Soda ...240       " 

Borax 120       " 

Glass 120       " 

Gave  only  63  grains  of  lead,  instead  of  about  120  for  which 
it  was  nitred. 

8th.  Ore 120   grains 

Nitr«' 130       " 

Litharge 480       " 

Soda 120       " 

Borax 120       " 

Glass ......80       " 

Gave  only  60  grains  of  lead,  but  remelted  with  another 
ounce  of  litharge  it  yielded  64  grains  additional.     A  ninth 


APPENDIX   TO   PART   ONE.  149 

trial,  with  similar  proportions  of  nitre  soda,  borax,  and 
glass,  but  with  2  ounces  of  litharge  in  the  first  melt,  gave 
a  satisfactory  button  which  was  not  weighed. 

In  assaying  arsenical  ores  by  the  second  system,  a  large 
quantity  of  iron  is  consumed.  The  presence  of  soda  di- 
minishes the  consumption  of  iron  by  sulphur,  but  not  by 
arsenic.  On  breaking  the  slag,  a  double  button  is  found, 
the  one  part  hard  and  brittle,  which  is  iron  arsenide;  the 
other  soft  and  malleable,  which  is  the  lead.  The  two  are 
easily  separated.  The  arsenical  button  contains  no  pre- 
cious metal,  but  if  the  ore  contained  nickel  or  cobalt,  that 
will  be  found  in  the  arsenide,  which  is  one  advantage  of 
the  second  system  over  the  first,  in  which  nickel  or  cobalt 
may  get  into  the  button  and  give  great  trouble.  Arsenic 
may  be  added  for  the  express  purpose  of  separating  nickel 
and  cobalt,  just  as  sulphur  is  for  copper. 

When  on  pouring  an  assay,  fluxed  according  to  the  first 
system,  it  is  found  that,  although  the  slag  is  sufiiciently 
liquid  (or  otherwise)  the  lead  is  scattered,  beads  of  it  cling- 
ing to  the  walls  of  the  crucible,  it  indicates  either  that  the 
assay  has  not  been  sufficiently  heated,  or  that  not  enough 
litharge  has  been  employed.  The  assay  may  be  at  once 
returned  to  the  crucible  from  the  mould,  provided  that  no 
part  of  the  slag  has  been  lost  by  overflowing,  and,  re- 
melted  with  the  necessary  correction,  it  can  then  be  cleanly 
poured. 

Some  readers  of  Part  I  have  objected  to  the  instruction 
there  given  to  heat  slowly  the  assay  by  scoriflcation;  they 
prefer  to  put  the  assay  at  once  into  the  highly  heated 
muffle.  Certainly,  in  the  case  of  oxidized  ores,  slow 
heating  would  be  a  waste  of  time,  and  with  some  sul- 


150  APPENDIX    TO   PART    ONE. 

phuretted  ores  it  may  be  unnecessary,  but  it  is  never- 
theless a  fact,  as  stated,  that  some  ores  cause  sputtering 
if  heated  suddenly,  and  my  aim  throughout  has  been  to 
keep  on  the  safe  side.  An  intelligent  workman  will 
soon  learn  to  modify  his  work  according  to  circum- 
stances. Another  suggestion  is  that  a  definite  rule  for 
the  proportion  of  water  to  be  used  to  moisten  the  bone 
ashes  for  cupels  would  be  useful.  Three  fluid  ounces  to 
the  pound  of  ashes  will  generally  answer.  Some  mix 
sifted  wood  ashes  with  the  bone  ashes;  others  use  a  little 
soda. 


APPENDIX   TO   PART   ONE.  151 


WEIGHING  BY    THE  OSCILLATIONS 
OF  THE  POINTER. 


On  page  72,  Part  ,  will  be  found  some  instructions  on 
this  subject.  There  are,  however,  two  methods  in  use, 
and  this  fact,  together  with  the  indefinite  manner  in 
which  the  terms  designating  the  position  and  movements 
of  the  pointer  are  used  by  different  writers  and  operators, 
has  caused  some  confusion  and  misconception  among 
students. 

The  one  method  is,  to  take  the  excess  of  movement  on 
either  side  of  zero  as  the  indication  of  the  excess  of  weight ; 
the  other  is,  to  take  the  distance  from  zero  at  which 
the  pointer  will  finally  rest  as  such  indication.  The  first 
method  will  give  twice  as  many  divisions  of  the  arc  as 
the  second,  hence  the  value  of  a  division  is  but  half  as 
much  in  the  first  as  in  the  second.  The  second  is  the 
method  given  in  Part  I. 

In  order  to  clear  the  subject  of  all  ambiguity,  I  pro- 
pose the  following  terms:  Range,  swing,  and  rest.  Range 
is  the  total  movement  of  the  index,  counted  in  divisions 
of  the  arc  (incorrectly  called  vernier  by  some).  Range 
may  extend  to  each  side  of  zero,  and  is  then  written  + 
and  — ,  plus  being  usually  the  right-hand  side,  minus  the 
left,  as  -h  5  —  o.     Or  range  may  extend  from   any  di- 


152  APPENDIX    TO   PART   ONE. 

vision  on  either,  side  to  zero,  as  +  5  —  0,  or  —  6  +  0. 
Again,  the  pointer  may  move  to  either  side  and  not  return 
to  zero,  as  +  7  +  3;  that  is,  the  pointer  goes  to  +  7  and 
comes  back  to  +  8,  or  —  7  —  3  on  the  other  side.  Range 
has  no  value  as  an  indication  of  the  amount  of  .prepon- 
derance, but  it  affords  a  means  of  calculating  swang  and 
rest. 

Swing  is  the  excess  of  movement  to  one  side  or  the 
other  of  zero,  caused  by  a  preponderance  of  v^eight  on 
one  of  the  pans;  hence  a  balance  in  equilibrium  will  have 
range,  if  the  beaui  be  set  in  motion,  but  can  have  no 
swing  in  the  sense  which  I  propose  for  that  term.  Swing 
is  equal  to  range  when  one  extreme  of  range  is  zero;  it  is 
the  difference  of  the  distances  from  zero  when  the  pointer 
goes  to  each  side  of  zero,  that  is  when  the  signs  oF  the 
distances  are  opposite;  it  is  the  sum  of-  the  distances  when 
the  signs  are  similar,  because  if  the  pointer  marks  +5 
and  comes  back  to  +3,  it  would  mark  +S  — 0,  if  the 
beam  had  impetus  enough,  or  +9  —  1,  etc.,  in  each  in- 
stance giving  swing  =  8. 

Range  is  a  matter  of  observation  only.  Swing  may  be 
a  matter  of  observation,  for  if  impetus  enough  be  given 
to  the  beam  to  make  the  pointer  move  to  right  and  left  of 
zero,  a  time  must  come  when  the  gradual  decrease  of 
movement  will,  practically  speaking,  cause  it  to  touch 
zero  at  one  extreme,  and  when  that  is  the  case  as  said 
above,  swing  is  equal  to  (identical  with)  range.  But 
swing  may  be  calculated  fi*om  observed  range  at  any  time 
when  the  beam  is  oscillatintr  as  shown  above. 

Rest  is  the  distance  from  zero  at  which  the  pointer  will 
stop   if  allowed   to   do   so.     In   this   sense,  a  balance  in 


APPENDIX   TO   PART   ONE.  153 

equilibrium  can  have  no  rest,  though,  as  before  remarked, 
it  may  have  range.  Rest  is  alv^ays  half  of  swing.  It 
may  be  observed  by  waiting  for  it,  or  it  may  be  known 
in  advance  by  finding  swing  and  dividing  that  by  2. 

Swing,  and  therefore  rest,  may  be  deduced  from  a 
single  observation  of  range,  but  more  accurately  from  the 
mean  of  several,  thus:  note  on  a  piece  of  paper  three  (or 
more)  extremes  in  one  direction,  and  the  intervening  two 
(or  more)  extremes  in  the  other  direction,  prefixing  to  each 
its  appropriate  sign;  find  swing  by  adding  the  means  to- 
gether if  the  signs  are  similar,  subtracting  the  lessei-  from 
the  greater,  if  the  signs  are  opposite.  In  the  first  case 
the  sign  of  swing  will  be  the  same  as  that  of  range;  in 
the  second,  it  will  be  that  of  the  greater  quantity.  Rest 
takes  the  same  sign  as  swing. 

Range  may  be  increased  whenever  desired  for  conven- 
ience, by  wafting  with  the  hand  a  slight  current  of  air 
against  either  of  the  pans,  after  which  the  case  must  be 
closed,  and  a  few  moments  allowed  to  elapse  before  be- 
ginning the  observation.  Examples:  Range  (an  average) 
is  4-8  — 3;  as  the  signs  are  opposite,  swing  is  the  difier- 
ence,  =  -j-5;restis  +2 J.  Again;  range  is  —8-1-3;  the 
signs  are  opposite  ^nd  swing  is  — 5;  rest,  —  2|.  Let  range 
be  -\-7-\-2;  the  signs  are  similar  and  swing  is  the  sum  = 
-f  9;  rest  is  H-4J.  If  range  is  +6  —  0,  swing  is  +6,  and 
rest  is  +3;  or  if  range  be  —6  +  0,  swing  is  —6,  rest  —3. 

The  value  of  swing  or  rest  for  the  balance  in  use  may 
be  found  by  trial  with  a  known  preponderance  of  weight 
on  either  pan.  It  varies  slightly  with  the  load  in  the 
pans.  Whether  the  preponderance  of  weight  indicated 
by  swing  or  rest  must  be  added  to  or  subtracted  from  the 
11 


154  APPENDIX    TO   PART   ONE. 

weights  in  the  weight- pan  miibt  be  left  to  the  conjmon 
sense  of  the  workman,  since  it  depends  upon  which  pan 
contains  the  object  to  be  weighed.  If,  however,  the  signs 
are  used  as  here  suggested,  and  the  object  be  on  the  left- 
hand  pan,  and  the  index  of  the  balance  points  downward, 
the  value  of  a  4-  swing  or  rest  must  be  added,  that  of 
—  subtiacted. 


APPENDIX   TO   PART   THREE.  155 


APPPENDIX  TO  PART  THREE. 


THE  ASSAY   OF   LEAD.         B^ctohlAmrj 


In  the  wet  assay  of  lead,  it  is  not  strictly  necessary  to 
filter  before  the  boiling  with  sodium  carbonate.  Digest 
with  nitric  acid,  or  with  nitric  and  sulphuric;  boil  off  a 
part  pf  the  acid;  add  sodium  carbonate  and  boil  twenty 
minutes;  test  the  liquid  with  red  litmus  paper,  which 
should  show  a  strong  alkaline  reaction,  otherwise  more 
soda  must  be  added  and  the  boiling  repeated.  Filter  and 
wash;  dissolve  the  carbonate  on  the  filter  by  pouring 
acetic  or  dilute  nitric  acid  on  it,  receiving  the  solution 
in  a  clean  vessel.  To  the  liquid  add  dilute  sulphuric  acid 
so  long  as  a  p.  p.  is  produced;  warm,  settle,  filter,  and 
wash  with  water  containing  s  dphuric  acid.  Dry,  ignite 
and  weigh.  If  the  ore  is  supposed  to  contain  strontium, 
smelt  the  p.  p.  with  potassium  cyanide,  and  weigh  the 
resulting  button  of  metallic  lead.  In  the  fire  assay,  the 
stirring  with  an  iron  rod,  as  directed,  is  only  necessary 
when  the  assay  contains  much  arsenic,  sulphur  or  anti- 
mony, the  object  being  to  avoid  the  inconvenience  of  the 
nails  sinking  beneath  the  slag.  The  heat  shou'd  not  h- 
so  high  as  in  assaying  for  gold  by  the  second  system,  but 
sufiiciently  so  to  make  a  liquid  slag. 


156  APPENDIX   TO   PART   THREE. 


THE  ASSAY  OF  COPPER. 


In  assaying  copper  ores  by  precipitation  on  iron  or 
zinc,  it  often  happens  that  a  sulphuretted  ore  as  well  as 
an  oxidized  one,  if  free  from  arsenic,  will  give  clean 
copper  without  the  treatment  with  ammonia.  Nitric 
acid  must  be  expelled  by  boiling  down  with  hydrochloric 
or  sulphuric  acid,  the  latter  if  lead  is  present.  When 
ammonia  is  used,  the  solution  need  not  be  first  filtered 
unless  much  silver  is  present,  in  which  case  the  assay 
should  always  be  boiled  down  with  sulphuric  acid,  be- 
cause silver  chloride  is  soluble  in  copper  chloride.  This 
applies  to  the  new  process  as  well  as  to  others. 

Sometimes  the  copper  comes  down  black,  while  an 
examination  of  the  ore  by  blowpipe  fails  to  reveal  any 
cause.  Resolution  and  precipitation  does  not  always 
give  a  properly  colored  precipitate.  This  may  have  been 
observed  by  other  assayers,  yet  I  find  nothing  about  the 
cause  or  prevention  in  the  books,  that  is  granting  that 
the  solution  is  made  as  directed.  I  have  succeeded  in 
cleaning  such  black  copper  by  re-dissolving  in  nitric 
acid,  precipitating  with  excess  of  caustic  potassa  solution, 
boiling,  filtering,  again  dissolving  the  black  oxide  in 
hydrochloric  acid,  and  precipitating  on  iron.  When  the 
ore  is  known,  by  former  experience,  to  be  of  this  char- 


APPENDIX   TO    PART   THREE.  157 

acter,  it  will  probably  answer  to  treat  the  first  solution 
with  caustic  potassa,  filter,  wash,  and  re-dissolve  in  hydro- 
chloric acid,  then  precipitate. 

The  assay  of  copper  by  the  new  method  may  be  made 
graviinetrically.  Prepare  the  solution  as  before  directed; 
precipitate  the  copper  by  a  slight  excess  of  potassium 
zanthate.  If  the  p.  p.  should  be  brown,  add  more  am- 
monia, and  it  will  soon  become  yellow,  unless  cobalt  is 
present,  in  which  case  proceed  as  before  directed  for  such 
contingency.  Settle,  filter,  wash,  first  with  hot  water, 
and  then  with  alcohol  of  95  per  cent,  until  the  drippings 
no  longer  become  turbid  on  addition  of  water.  Dry  on 
the  filter  at  the  heat  of  boiling  water.  The  p.  p.  may 
be  removed  from  the  filter,  for  the  weighing,  with  but 
little  loss,  or  it  may  be  weighed  on  a  tai-ed  filter.  Cal- 
culate 33  per  cent  of  the  net  weight,  as  copper,  or,  if  not 
too  p  irticular,  take  one-third. 

Note. — I  regret  that  the  system  which  I  now  propose, 
of  weights  to  be  taken  for  the  assay  of  certain  sub- 
stances, did  not  occur  to  me  until  nearly  the  whole  of 
the  foregoing  matter  had  not  only  been  written,  but  also 
printed.  There  is  an  example  of  the  method  in  '*  Leach- 
ing Gold  and  Silver  Ores,"  in  the  "  Assay  of  Manganese," 
and  one  in  the  "  Assay  of  Salt,"  in  the  present  book,  and 
it  was  while  thinking  over  the  latter  that  the  idea  oc- 
curred to  me  of  a  general  application.  In  all  those 
methods,  in  which  the  substance  got  is  difierent  from 
that  sought,  the  practice  has  been  to  state  that  the  former 
contains  so  much  per  cent,  of  the  latter,  or  the  weight 
got  must  be  multiplied  by  some  number,  which  is  often 
an  inconvenient  one,  in  order  to  ascertain  how  much  of 
the  substance  sought  was  present  in  the  assay. 


158  APPENDIX    TO   PART   THREE. 

It  is  inuth  simpler  to  take  such  a  weight  of  the  assay 
substance  as  would,  if  it  consisted  wholly  of  the  sub- 
stance sought,  give  100,  by  similar  weight,  of  the  sub- 
stance to  be  got  and  weighed.  The  .weight  got  would 
then  be  the  percentage  of  the  substance  sought  which 
the  assay  contained.  In  the  wet  assay  of  lead,  for  ex- 
ample, when  not  the  lead  itself  but  the  sulphate  is  to  be 
weighed,  as  lead  sulphate  contains  08.33  per  cent,  of 
lead  it  is  easily  seen  that  68.33  parts  of  pure  lead  would 
give  100  parts  of  sulphate,  and  68.33  parts  of  a  sub- 
stance'which  is  only  partly  lead  would  give  so  much 
sulphate  as  would  correspond  to  the  percentage  of  lead 
in  it. 

In  case  the  quantities  should  be  inconveniently  large 
or  small,  in  the  system  of  weights  used,  we  may  take  a 
simple  multiple  or  an  aliquot  part  of  the  whole,  and 
divide  or  multiply  the  weight  got  accordingly  by  some 
simple  number. 

Following  are  the  weights  of  ore,  etc.,  to  be  taken  on 
this  system  to  be  assayed  for  the  respective  substances 
weighed  in  the  forms  named.  The  weights  may  be 
grains,  hundredths  of  grains,  grammes,  milligrams,  etc., 
as  may  be  convenient;  the  weight  got  being  stated  in 
similar  terms  is  the  percentage  of  the  substance  sought. 
68.3  for  lead  as  sulphate. 

36.5  for  zinc  as  ammonio  phosphate. 
79.0  for  copper  as  oxide. 

33.0  for  copper  as  zanthate. 

19.6  for  nickel  and  cobalt  as  zanthate. 
13.8  for  sulphur  as  barium  sulphate. 

23.15  for  arsenic  as  metallic  silver  by  substitution. 


APPENDIX   TO   PART   THREE.  159 

Whenever  an  assay  of  any  kind  is  undertaken,  a 
record,  or  at  least  a  memorandum,  should  be  made  of  the 
quantity  operated  on,  and  any  other  particulars  which 
require  to  be  kept  in  sight.  In  cases  of  rather  complex 
operations  it  is  a  good  plan  to  write  down  the  entire 
proposed  course  of  treatment,  and  to  check  off  each  step 
as  it  is  performed;  especially  should  this  be  done  when 
variations  from  the  prescribed  course  are  contemplated, 
as  will  often  occur  if  the  workman  is  intelligent,  and  has 
some  knowledge  of  chemistry. 

When  a  multiple  or  aliquot  p'art  of  a  standard  quan- 
tity is  taken,  the  fact  should  appear  on  the  record ;  for 
example,  in  the  copper  assay  where  the  copper  is  to  be 
weighed  as  zanthate,  33  grains  would  be  too  much  of  a 
rich  ore,  giving  a  too  great  volume  of  p.  p.  for  rapid 
working.  A  tenth  of  the  quantity  will  suffice  in  such 
a  case,  and  may  be  written  f  f  grains,  in  order  to  show 
that  the  weight  of  copper  zanthate  got  in  grains  is  to  be 
multiplied  by  10  for  the  percentage,  because  33  grains 
of  copper  would  give  100  grains  of  zanthate.  On  the 
other  hand,  if  gramme  weights  were  used,  33  grammes 
would  be  too  much  of  any  ore,  and  33  milligrammes 
would  be  too  little  of  any.  In  this  case  -^  grammes= 
330  milligrammes  might  answer,  and  should  be  entered 
in  the  form  of  a  vulgar  fraction  as  a  reminder  that  the 
p.  p.  weight,  in  grammes,  is  to  be  multiplied  by  100;  or 
it  might  be  33x10  mgs.,  which  would  indicate  that  the 
p.  p.  weight,  stated  in  mgs.,  must  be  divided  by  10.  A 
little  practice  will  give  facility  in  this  system  of  weigh- 
ing, and  the  rule  for  the  weight  to  be  taken  is,  that  it 
should   be  numerically  equal  to  the  percentage  of  the 


160  APPENDIX   TO   PAKT   THREE. 

substance  sought  contained  in,  or  indicated  by,  the  sub- 
stance got.  In  the  assay  of  manganese  for  chlorination 
works,  the  substance  sought  is  manganese  binoxide;  the 
substance  got  (weighed)  is  carbon  dioxide,  and  99  of  the 
former  are  indicated  by  100  of  the  latter,  hence  we  take 
99  of  the  assay  substance.  In  the  arsenic  assay,  as  here 
given,  arsenic  is  sought  and  silver  is  got;  100  of  silver 
in  this  case  indicate  23.15  of  arsenic,  and  we  take  23.15 
or  ^x^'  grains  of  the  ore.  In  the  copper  assay,  if  we 
are  going  to  precipitate  the  copper  in  the  metallic  state, 
copper  is  sought  and  copper  is  got,  and  copper  of  course 
contains  100  per  cent,  of  copper,  so  we  take  100  of  ore 
in  any  convenient  term  of  weights,  or  we  take  Vi?  V^^~ 
haps ;  but  if  we  are  going  to  get  the  copper  in  the  form 
of  oxide,  containing  79  per  cent,  of  copper,  we  take  79 
of  ore  or  ~,  79x10,  etc.,  according  to  the  estimated  rich- 
ness of  the  ore  and  the  denomination  of  the  weight. 

The  system  is  not  applicable,  or  at  least  is  not  specially 
advantageous  when  two  or  more  substances  are  to  be 
deter'mined  from  one  assay  quantity,  unless  all  are  to  be 
weighed  in  forms  which  have  equal  percentage  values. 
This  is  the  case  with  nickel  and  cobalt  when  weighed  as 
zanthates. 

In  conclusion  it  is  proper  to  explain  that  methods  are 
subject  to  modification,  and  even  to  total  change,  often 
with  a  saving  of  time  and  labor,  under  the  varying  con- 
ditions presented  by  difference  of  composition  of  the 
substance  treated.  I  have  given  a  few  of  these  modi- 
fications; to  give  them  all  would  be  to  write  a  good  sized 
volume  on  each  assay.  My  aim  has  been  to  give,  first 
and  more  particularly,  a  process  which  is,  as  nearly  as 


APPENDIX   TO   PART   THREE.  161 

may  be,  sufficient  for  any  probable  case  within  the  scope 
of  my  plan ;  to  enable  the  student  to  reach  a  reasonably 
accurate  result,  even  though  not  in  all  cases  by  the 
shortest  road.  In  the  assay  of  lead  or  copper,  for  in- 
stance, there  are  many  methods  which  could  not  be  given 
in  a  book  of  the  size  and  price  of  this.  Those  who  de- 
sire to  study  other,  and  I  freely  admit,  for  certain  cases, 
better  processes,  may  find  them  described  in  other  and 
more  pretentious  works.  This  book  is  not  designed  for 
the  use  of  students  who  enjoy  the  advantages  of  pro- 
fessional instruction,  but  simply  for  that  of  people  who 
want  to  assay,  whether  for  business  or  pleasure. 

Some  defects  in  the  arrangement  of  matter  may  be 
ascribed  to  the  circumstance  that  considerable  addi- 
tions to  the  manuscript  were  made  while  the  writer 
was  at  a  distance  of  more  than  a  thousand  miles  from 
the  first  written  portions,  and  some,  as  well  as  altera- 
tions, while  the  work  was  in  press. 

My  thanks  are  due  the  gentlemen  of  the  Pacific  Press 
Publishing  Company  for  their  efforts  to  oblige  me  under 
conditions  which  must  have  caused  them  some  annoy- 
ance. 


JUSTINIAN  CAIRE, 

IMPORTER  AND  DEALER  IN 

Assayers'  Materials  g  Chemieals, 

MILL  SUPPLIES  OF  ALL  KINDS 


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Opera*,  Field,  and  Marine   Glasses, 
Optical  Goods, 
Aneroid  and  Altitude  Pocket  Barometers, 

Miner's  Compasses,  Drawing"  Instruments,  Etc. 

SS"  Specialty  of  Goods  for  Chlorination   Works,  j^ 


BRASS  AND  STEEL  BATTERY  SCREENS, 

And  all  kinds  of  wire  work  made  to  order. 

521  and  523  Market  Street,  and  16  to  22  Stevenson  Street, 

SAV  FRA]SrCI8CO,  CAL. 

SM  Catalogues  and  Price  Lists  on  application. 


[From  tlie  Mining  and  Scientific  Prexs.\ 


A  PLAIN  BOOK  ON  ASSAYING. 

"ASSAYING  GOLD  AND  SILVER  ORES." 

By  C.  H.  Aaron. 


PART   I. 


The  author  of  this  work  is  wall  kuowa  in  the  mining  regions  of  the 
Pacific  Coast  as  a  practical  mjtallurgist  of  many  years'  experience.  His 
writings  for  the  press  and  his  two  previous  works  ("Testing  ami  Work- 
ing Silver  Ores,"  and  "Leaching  (xold  and  Silver  Ores")  have  shown  his 
ability  as  a  writer.  The  little  book  is  plainly  and  simply  written,  more 
especially  for  the  use  of  those  persons  not  familiar  with  chemistry.  JN"© 
symbols  are 'used,  everything  being  plainly  stated  and  clearly  described. 
The  scope  of  the  book  is  shown  in  its  table  of  contents,  as  follows:  Tn- 
troductioa;  Implements;  Assay  Balance;  Materials;  The  Assay  Office; 
Preparation  of  the  Ore;  Weighing  the  Charge;  Mixing  and  Cliarging; 
Assay  Litharge;  Systems  of  the  Crucible  Assay;  Preliminary  Assay; 
Dressing  the  Crucible  Assays;  Examph'S  of  Dressing:  The  Melting  in 
Crucibles;  Scoritication;  Cupellation;  Weighing  the  Bead;  Parting;  Cal- 
culating the  Assay;  Assay  of  Ore  Containing  Coarse  Metal;  Assay  of 
Eoasted  Ore  for  Solubility;  To  Assay  a  Cupel;  Assay  by  Amalgamation; 
To  Find  the  Value  of  a  Specimen;  Test  for  Ores;  A  Few  Special  Miner- 
als; Solubility  (»f  Metals;  Substitutes  and  Exp  clients;  Assay  Tables. 
These  assaying  tables  give  simple  directions  for  figuring  out  results. 
This  is  the  simplest,  cheapest  and  most  easily  comprehended  work  on 
Assaying  yet  published  The  volume  comprises  105  pages,  with  illus- 
trations, and  is  well  feound  in  cloth.  The  price  is  |1,  postpaid.  Pub- 
lished by  Dewey  &  Co.,  Miking  and  Scientific  Press  office,  San 
Francisco — 1 884. 

N.  B.  — The  above  refers  to  Part  I,  which  preceded  the  issue  of 
this  book,  i.  e.,  Parts  II  and  III. 

AARON'S 

LEACHING  GOLD  AND  SILVER  ORES. 


The  most  complete  hand  book  on  tbe  subject  extant; 
164  pages  octavo.  Illustrated  by  twelve  lithographic  en- 
gravings and  four  wood  cuts.  Fully  indexed.  Plainly 
written  for  practical  men.     In  cloth,  $3.00.     Sold  by 

DEWEY  &  CO., 

Mining  and  Scientific  Press  Office, 

San  Francisco,  Cal. 


,iitll©  Pi©is  Fit 


BUSINESS  ESTABLISHED    1860. 


Our  United  States  and  Foreign  Patent  Ajrency 
presents  manj-  and  important  ad\antages  as  a  Home 
At>eni.y  over  ail  others,  by  reason  of  long  establish- 
ment, great  experience,  thorough  system,  intimate 
acquaintance  with  the  subjects  of  inventions  in  our 
own  community,  and  our  most  extensive  law  and 
reference  library,  containing  official  American  and 
foreign  reports,  files  of  scientific  and  mechanical 
publications,  etc.  All  worthy  in  entions  patented 
through  our  Agency  will  have  the  benefit  of  an  illus- 
tration or  a  description  in  the  jflmiiig  and 
*oieiitilic  Pim»ws.  We  transact  every  branch 
if  patent  business,  and  obtain  patents  in  all  coun- 
ries  which  grant  protection  to  iinentors.  The 
large  majority  of  United  States  and  foreij;n  patents 
issued  to  inventors  on  the  Pacific  Coast  have  been 
obtained  through  our  Agency.  We  can  gi\  e  the  best 
and  most  reliable  ad\ice  as  to  the  patentabdity  of 
new  inventions.  Our  prices  are  as  low  as  any 
first-class  agencies  in  the  Eastern  S  ates,  while  our 
advantages  for  I'acific  Coast  Inventors  are  far  supe- 
lior.     ^i^  Circulars  of  advice  free. 

Address  J>K\VKY  &.  C<>.  (A.  T.  Dewey,  W.  B. 
Ewer,  Geo.  H.  Strong),  Patent  Agents,  252  Market 
Street,  San  Francisco. 


ROLLER 

Ore  feeder 

Patented  May  28,  1882. 


The  Most  Perfect  Machine  for  Feeding  Ore 
to  Stamp  Mills  ever  invented. 


Golden  State  &  Miners' 
IRON  WORKS. 

Manufacture  of 

Castings  and  Machinery 

Of  All  Descriptions. 

Mining",  Milling,  and  Dredging 
Machinery  a  Specialty. 

Nos.237  to  261  First  St.,  S.  F. 


Mining  and  Scientific  Press. 

The  Best  Practical  MINiNG-  Journal  in  the  World. 


Established  in  1860,  this  paper  has  been  eminently  successful  as  a  popular  and 
useful  milling  and  mechani  al  journal.  fielative  to  precious  metals  especially, 
it  is  the  leadinsr  mining  paper  of  the  world.  Among  its  contributors  are  some  of 
the  busf.  mining,  scientific,  and  mechanical  writers  in  the  United  States,  including 
the  author  of  thif  book. 

It  is  largely  patronized  by  the  leading  Miners,  Mine  Owners,  Superuitendents, 
Engineers,  Metallurgists,  Chemists,  M mufacturers.  Mechanics:  Scientific,  Profes- 
sional, and  Industrial  "  Men  of  Progress"  on  the  Pacific  Coast;  and  many  leading 
Mining  Men  throughout  the  mining  fields  of  the  world. 

It  is  by  far  tlie  best  advertising  medium  in  the  Pacific  States  and  Territories 
for  Mining,  Mechanical,  Engineering,  Building,  and  Manufacturing  Tools  and  Imple- 
ments, Goods,  Supplies,  etc 

Being  thoroughly  able  and  reliable  in  its  editorial  and  business  management, 
and  1  ng  established  in  the  most  progressive  industrial  portion  of  the  Union,  at 
present,  its  p  iwer  as  an   advertising  mediun  is  unsurpassed. 

Subscription,  S3.00  a  year.  Adveitising  rates,  moderate.  Send  for  samples  and 
further  information. 

DEWEY  &  CO.,  Publishers, 

2J2  Market  Street,  San  Francisco. 

MINING  BOOKS^ 

All  valuable  Mining  and  Metallurgical  books  issued  on  the  Pacific  Coast  are  for 
sale,  wholesale  and  retail.     Also,  other  desirable  mining  publications. 

Address, 

DEWEY  &  CO., 

Mining  and  fi^cientiilc  Press  Office,      SAX  FRAXCI^iO,  €AI.. 

C.  A.  LucKHARDT,  Manager.  Established  1869. 


OF  SAN  FRANCISCO. 
Ores    Crushed    and    Sampled   and   Working   Tests    Made 

BY  AXY  PROCESS. 
ASSAYING  in  all  its  Branches. 
ASfAIiYSlS  ofOBKS,  Minerals,  IVater,  Soils,  Products,  Etc. 

Formerly  Huhn  &  Luckuardt, 

MINING  ENGINEERS  AND  METALLURGISTS, 

23  Stevenson  Street,  Near  first  and  Market  Streets. 


850. 


885. 


RANKIN,  BHAYTON  &  CO., 

San  Francisco,  Chicago,  and  M\  York. 


BUILDERS  OF 


Mining  Machinery 


Plants  tor  Gold  aud  Siivei  jli.l:,,  cuibiaciiig  t.-.o  latest  and  most  improved  tnachinery  and  processes 
for  base  and  tvue  '>res.  Water  Jacket  S.neLin^  Furnaces  tor  Sil.e  ,  Lead,  and  Copper  Ores,  with  new 
an  1  important  improv-emjnts,  saperi  )r  to  any  tier  mai<e.  H  nsting  Works,  Punping'  Machinery, 
C  il  Jri  Uzin^  Fu:-ni  es,  eD  •.  vVi  >  fer  our  JUit  >;ner'3  the  hesc  resuUs  of  thirty  years' experience  in 
thisspe  ial  line  or  bu'siness,  and  aie  prepared  to  lUi-nish,  either  from^an  Francisco  or  Uhicayo,  the 
m  (s^appr  )ve  1  character  of  Mining  an  I  RjJu  ;t  on  Vlach  nery,  superior  in  design  and  construction  to 
that  of  any  other  make,  at  t  le  1  ).vest  jio-sible  prices.  We  also  c  >ntract  to  deliver,  in  complete  run- 
ning order.'Milis,  Far-ni  -o-;,  Hosting'  Works,  eDc,  in  a'<y  of  the  minin,^  States  and  Territories.  Esti- 
mates given  ofi  apjjlication. 

Beyond  question  the  cheapest  and  most 
eflfective  machine  of  the  kind  now  in  use, 
adapted  to  a  1  jfrades  and  vlassesof  oses.  Tins 
machine  has  been  thoroughly  testeil  for  the 
past  two  years  under  a  great  variety  of  condi- 
tions, si\ing  most  extraordinary  results,  far  in 
advance  of  anything  before  realized. 

A  recent  competitive  test  made  with  the 
Frue  at  the  Carlisle  mine  in  New  Mexico 
showed  an  advantage  of  30  per  cent,  in  favor 
of  the  Dun  'an,  the  amount  saved  over  the 
Frue  being  sufficient  to  pay  the  entire  cost  of 
the  machines  nearly  every  month  in  the  year. 


For  Galena,  Silver,  and  Copper  Ores. 


Th, 

the  crn 


The  Pacific  Water  Jacket  Smelters  emb'ace 
many  features  tliat  are  entirely  new  and  of 
great  practical  utidty,  which  are  covered  by 
letters  patent.  No  other  furnace  can  compare 
with  these  for  durability,  and  in  cajiacity  for 
ujiinterrupied  work. 

More  than  one  hundred  and  fifty  of  them  are 
now  running  on  the  Pacific  Coast,  givina:  results 
never  before  obtained  as  regards  continuous 
running,  economy  of  fuel,  grade  and  quantity 
of  bullion  produced.  We  are  prepared  to  dem- 
onstrate by  facts  the  claims  here  made. 

■  Smelter*!  are  shipped  in   a   complete  state,  requiring  no  brick  or  stone  work,  except  that  for 
cihle,  thus  savim;:  '.rreat  expense  nnd  loss  of  time  in  construction . 


BAKER'S  MINING  HORSE-POWER. 

The  most  efl^icient  and  practical  machine  ever 
invented  for  the  service  of  prospectors  and  others 
requiring  the  use  of  a  horse-p  'wer.  Possessing 
all  the  requirements  of  a  first-class  hoist,  and  af- 
fording mean-^  for  the  con  inuous  operation  of  a 
Pump  or  Blower,  without  interfering With  a  hoist- 
ing apparatus. 

It  is  made  entirely  of  iron;  no  piece  weighs  over 
300  pounds.  At  the  ordinary  speed  of  a  horse  a 
1,000  pound  bucket  of  ore  may  be  raised  120  feet 
per  minute.  The  hoisting  drum  is  under  the 
complete  control  of  the  man   at  the  shaft,  and  is 

capable  of  carrying  five  hundred  feet  of  fi\e-eighths  steel-rope.    The  cost  of  erection  is  slight,  as  two 
men  in  half  a  day  can  easily  put  it  in  place,  readj'  for  work. 

While  this  power  is   more   panimla'lv  for  mining  purposes,  it  is  equally  adapted  to  all  other 
uses  where  animal  power  is  required.     AW  SEND  FOR  CIRCULAR. 


PACIFIC  IRON  WORKS, 


San  Francisco,   ) 
Chicago,  &  N.  Y.  f 


RANKIN.  BRAYTON  &  CO., 


Gold  Quartz  and  Placer  Miners. 

I  Silver-Plated 

«fe-  AMALGAMftTING 

PLATES, 

FOR  SAVING  GOLD. 

S^  First  Premium  awarded 
at  MECHANICS'  FAIK,  1884. 

Every  iJescriptiDii  of  Plates 
for  Quartz  Mills  and  Wet  or 
Dry  Placer  Amalgamator  Ma- 
chines made  to  order,  Corru- 
gated or  Plain.  Over  2,0<)0 
orders  lilled.  The  most. ex- 
tensive and  successful  manu- 
facturer of  these  Plates  in  the 
United  States.  Will  fill  orders 
for  (ielivery  in  Rocky  Moun- 
tain and  I'acilic  (.oast  Mining 
St>ites  at  lower  prices  than 
any  other  nianufacturer. 

Old  .Mining:  Plates replated. 

Old  Plates  bought  oi  gold 
separated  for  low  percentaj.'e  of  result.     SEND  FOR  PRICE  LIST. 

San  Francisco  Platins  f  oris.      E.  &,  DENNISTON,  ProB'r. 

05  t  and  4»5.>  .llisfsioii  St.,  Han  Fi*anci!>ico,  €al. 


F.  A.  HUNTiNCTOM'S  CENTRIFUGAL  ROLLER 
QUARTZ  MILL. 

The  Huntington  Mill  has  i)assed  entirely  thr  m<h  the  experimental  stage.  Three 
years  of  continuous  use  at  a  number  of  mint  s  in  California  has  enabled  the  in\  entor 
to  perfect  and  improve  the  machinerj'  until  he  feels  justified  in  assuring  the  public 
tliat  he  has  reached  the  absolute  in  the  construction  of  a  perfect  quartz  mill. 

We  hereby  explain  theaccom 
panning  cut: — 

The  ore  and  water  being  fed 
into  the  mill  at  the  hopjier  A, 
the  rotating- rollers  and  scrapers 
thro\v  the  ore  against  the  ring- 
die,  where  it  is  crushed  to  any 
desired  fineness  bj-  the  centrif- 
ugal force  of  the  rollers  as  they 
pass  over  it. 

•  The  water  and  pulverized  ore 
are  thrown  against  and  through 
the  screens  wheji  fine  enough. 
The  (iischargf  is  so  perfect  that 
it  makes  little  or  no  slimes  and 
leaves  the  pulp  in  good  condition 
for  concentrt^tion.  The  rollers 
are  suspended,  leaving  a  space 
of  one  incli  between  them  and 
the  bottom  of  the  mill,  thus  al- 
lowing them  to  pass  freely'  over 
the  quicksilver  and  amalgam, 
without  grinding  it  or  throwing  it  from  the  mill,  while  it  agitates  it  sufficiently  to 
make  amalgamation  perfect.     For  wet  crushing  and  «oM  saving  it  has  no  equal. 

F.  A.  HUNTINGTON,  46  Fremont  St.,  San  Francisco. 


SELBY  SMELTING  and  LEAD  CONIP'Y, 

416  Montgomery  St.,  San  Francisco. 


GOLD  AND  SILVER  REFINERY 

AND  ASSAY  OFFICE. 


Highest  Prices  Paid  for  Gold,  Silver,  and  Lead 
Ores  and  Sulphurets- 


ManTrs  of  Bluestone.  t^lZtA^^.If!i' 


Shot,  Babbitt  Metal,  Solder,  etc. 


EDWARD  KEATING.  CHRIS.  FAGAiS^. 

California  Electro  Plating  Works, 

657  MISSION  STREET, 

Bet.  New  Monta^omery  and  Third,    -    ■    -    SAN  FRANCISCO- 

S.lverPIat3dCopp3r  Plates  ^IpSl^/y^ 

GOLD,  SILVER,  and  MCKEL  PLATLVG  on  all  Metals. 

KEATING  &  FACAN,     -      Proprietors. 

iSSillE  MS  AmiimhL  CHIMIST, 

1  13  LEIDESDORFF  STREET, 

Bet.  Calirornia  and  i^acramcnto  ii^ts.,  i^AK^  FRAMCISCO,  Cal. 

impersonal  Attention  Insures  Correct  Returns."^ 


"TRIUMPH"  ORE-CONCENTRATORS. 

$1,000  CHALLENGE  ACCEPTED! 

PRICE:   FIVE  HUNDRED   AND    FIFTY    DOLLARS 

($550.OO)    F.    O.    B. 

Mining  men  are  hereby  notified  that  there  are  no  existing  patents  on  the  shaking 
motion  as  applied  to  belt  concentrators— the  side  shake  of  the  Fnie  machine  havij  g 
expired  July  9,  1884  The  Embrey  machine  has  no  patent  on  the  end  shake.  The 
patents  on  the  Triumph  Concentrutor  do  not  in  any  manner  conflict  with  those  of  any 
other  machine,  and  they  are  in  all  respects  better  machines  than  either  tiie  Frue  or 
Embrey, 


Awarded  the  Medal  of  Superiority  at  the  Exposition  at  Denver,  Col- 
orado, 1884,  in  Competition  with  the    "Frue"   Vanner, 
the  "  Embrey  "  Machine  and  the  "  Rouse  "  Tables. 

The  superiority  of  the  present  construction  of  the  "  Triumph"  over  the  form  orig- 
inally introduced,  together  with  the  demonstrated  results  all  trials  had  with  the  Frue 
Vanners,  induce  us  t  >and  we  hereby  accept  the  challenge  of  f  1,000,  flaunted  by  the 
agents  of  the  "  Frue  Vanning  Machine  Conpaiiy,"  and  hold  ourselves  in  readiness  to 
enter  into  a  competitive  trial  for  that  sum,  at  such  place  and  upon  such  terms  and 
conditions  as  may  hereafter  bo  mutually  arranged. 

We  guarantee  purchasers  against  all  costs,  expenses  or  charges  incurred  b.v  reason 
of  any  infringements  of  any  existing  patents. 

JOSHUA  HENDY  MACHINE  WORKS, 

Nos.  39  to  51  Freraoat  Street,        San  Francisco,  Cal. 


$1,000  CHALLENGE! 


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THE  FRUE  ORE  CONCENTRATOR,  or  Vanning  Machine 


